Wouldnt put too much emphasis on that video as it seems Xavi is still evolving his ideas.
Of course Xavi is still learning and evolving as a manager. And as you said in other post his system is fluid so could easily change between different formations just making a sub or changing players roles a bit. I think his ultimate goal is to become tactically flexible and adapting to different opponents but as of now he's still quite limited by the squad he has. New signings will give him a chance to explore new options to get the best out of the team.
The main reason I've mentioned a possibility of 343 is because we have a lot of good midfielders (with Kessie and Torre incoming) and this would give them enough playing time to keep them happy longterm. Another reason is our options at FB are also limited. Alves will be 40, Xavi doesn't seem to rate Dest, Roberto will probably leave (at least he should) and on the left we have an aging Alba with no backup. So it's very likely over next 2 years we'll possibly need to bring 3-4 new FBs in a market that's very limited. Sure, maybe Dest will stay and turn into a great player, maybe Gaya/Grimaldo can be brought for cheap and be solid contributors at least for a few years until we find someone better, maybe Balde can become a good backup at least after getting a year of experience on loan and maybe we'll sign that Deportivo kid and he'll turn out the next Pedri (in terms of his immediate impact/quality not positional wise ofc). But none of that is guaranteed.
While people are talking about more immediate needs like a top striker and a CB I think where we could struggle more mid and longterm is to find quality options on the market at both FB positions. Just because there is an overall lack of quality at those positions. I'm not saying it's not possible to find a good RB or LB, possibly even for cheap but I think there are just more quality young CBs available. France/Ligue 1 are producing them in abbundance every year, we just need to find and sign them before other big clubs get to them and they become either too expensive or unavailable at all.
So just maybe mid term (over next 2-3 years) thinking about commiting to 343 is at least worth a consideration. Of course even if Christensen will turn out good we'd still need another starting quality CB alongside him and Araujo and another one or two for depth. Garcia could be kept around as a 5th/6th CB in that case.
As for next season it's clear we don't have enough quality nor depth to play 343 full time so 433 will stay a primary system. That doesn't mean we couldn't play with 3 atb in certain games though.
3-4-3 is a harder system than it seems. And in most aspects, it's just not worth it. It's also deceiving in the sense that you don't necessarily play more offensive with it.
Play the shit out of the 4-3-3 and make the players dream the positions in their sleep.
It's not about playing more offensive but giving Xavi more tactical flexibility and as he explained in that video I've posted using 343 to gain a numerical superiority against teams playing 442.
He's a young, hard working manager with (I believe) a lot of innovative ideas so I think his plan is to build a very versatile and flexible squad (especially when amigos will finally leave). We shouldn't stick with 433 for historical/emotional reasons or just for the sake of it. Until it works it's great but if it won't sometimes we should have other solutions prepared. And that's something I think Xavi is also thinking about when (re)building the team for next season(s) together with Alemany and Jordi.
He clearly has his philosophy he fully believes in but is a lot less stubborn than I was affraid of before he was hired. He got the most out of someone like LDJ who is probably the most anti-Barca/Xavi DNA player we could imagine. And he's mostly using Auba to utilise his strenghts despite him also being less than ideal for possession based football.
Besides veterans (who should be out of the club within 12-24 months anyway) most of our squad is already quite flexible. Araujo is learning to play RB although obviously shouldn't be anything more than an emergency starter there or in special circumstances to cover most dangerous player of the oppoents - Vinicius in El Clasico, Kostić yesterday (preferably we'll get a RB able to do that job though). Also has some experience playing in a 343, the same as Garcia. Dest (if he stays longterm) can play both RB/LB.
Frenkie can basically play any role in midfield and also as a CB if needed or if Xavi would conside that from a tactical standpoint. Pedri and Gavi can play their usual CM/AMC roles or also be set up wider in midfield if needed. Pedri has played as LM/LW in Las Palmas and Gavi was used a false 9 sometimes, even for Spain in NT IIRC. I know playing with a false 9 is not something Xavi seemingly wants to do right now but could consider that in future depending on players we'll have. Torre (to not go fully OT in his thread) can also be used multiple ways once he adapts to the team and if proven good enough. Also curious how Xavi plans to use Kessie but I'm sure he already has a pretty good idea about that.
One of the reasons we brought Ferran was imo his versatility. For now he found his place at LW but I'm sure longterm Xavi will give him a chance upfront and on the right again as well. Still a work in progress and needs to be polished but has brutal upside. Ansu can play on the wing or upfront if finally stays fit. Auba can also be utilised on the wings if we bring a top striker. Dembouz (if he stays) can play right or left.
You see my point?
Could be wrong but this is what I believe Xavi will try to do longterm. Players capable of playing in different roles/positions, use different combinations of them that would fit certain opponent the best etc. Or in worst case be prepared for injuries but hopefully we'll have more luck next season and his squad selection will be based more on form/tactical decisions than just pure availability of players.
He clearly didn't have time nor the players to experiment much this season when he took over and we've played likes of Abde and Jutgla upfront. First he needed to lift the team morale (and the best way to do that is to win, even "ugly") and improve them physically (as much as this can be done during the season he did a good job). And then he had to teach some players basics of the possesion football and pressing.
But in July he'll have three full weeks of trainings to implement new ideas to improve the team. From that POV having no big tournament this summer should help us as most players should be there to start preseason. And this is even more important for new signings so it's good we're doing a lot of early work in that aspect and hopefully our squad will be as good as done in early July when team will get back together.
Surely we won't be able to offload everyone we want to that point but at least some players should leave before end of June (from financial standpoint moreso than from a sporting one although wouldn't really like to have 6-8 players with no spot in the team next season still be here at start of preseason) and most if not all new signings should be done imo.
So I believe we'll see an even better and a bit different team (not just in terms of personell but also some tactical tweaks) next season but this still won't be the end product. We'll need another season of growing and then another good to great transfer window in 2023 (hopefully with less financial restrictions that we'll still need to deal with this summer). Of course that doesn't mean I don't believe current team improved with likes of Christensen, Kessie, maybe Raphinha and hopefully a healthy Ansu can't at least challenge RM (even with Mbappe and/or Haaland) for La Liga next year. I also believe we would be much more competitive against teams like Liverpool or Bayern but still probably not there to actually beat them. But we'll see how the team will look in September. Now focus should be on finishing current season strong and then bring that momentum into next year.