For me Sevilla and Villarreal have the best squad depth in La Liga. Two quality players in each position. Both teams also have a lot of experience and key veterans still performing on a good level unlike our old core. And obviously they have coaches who know how to use what they have at their disposal.
Managers work is to do the best with what they have, no to assembly the squad. The later starts from above the manager, from sporting directors who are actually the manager 's boss.
That is the difference between Seville who had Monchu on their disposals and us who had 6 or whatever number of guys in past 7 years.
Don't disagree with your point but tbh I think Lopetegui has also played an important role in building of this current Sevilla team. Monchi is bringing him players he wanted to fit into his system. Proven/experienced and mostly physical players. If Lope didn't like them he just didn't play them (like Koeman).
Monchi made some risky big money signings and while Kounde for 25m (and several others like Ocampos, YEN, D.Carlos, Jordan who also cost around 15-20m) clearly turned out great OTOH he has spend 25m on Rony Lopes who never got a chance from Lopetegui and is now on his third loan spell. Oussama Idrissi is a similar example. Monchi has paid 12m for him in 2020, he had a few cameo appearances for Sevilla before being send on loan to Ajax in January where he also barely played. Despite having a good preseason they've probably had no serious offers to sell him so he stayed, started first game against Rayo, was subbed off at HT, then played 26 minutes in next two games and hasn't played since as Lopetegui prefers Suso, Lamela (who had a good start of the season) and Ocampos (has missed a first few games but is now back) as his wingers.
Monchi admitted in an interview some time ago that at first he didn't know what exactly Lopetegui is looking for (and that's probably a main reason for failed transfers like R. Lopes) but now after working with him for years he knows much better so it's easier for him (and his scouts) to go after players that fit Lopetegui's profile better.
Another thing is since WBY for 40m to Monaco in 2019 they've not sold a key player for big money in last two years. Surely, Bryan Gil went to Tottenham this summer but he was on loan last year and not in their first team plans. They've kept Kounde despite interest from Chelsea. We'll see if they can keep him until the end of the season or he'll be sold in January. So they've basically kept their team together for two seasons now and their net spent (I know teams are not looking at finances from that standpoint) since summer 2019 is more than 100m.
And this summer they've added more depth as their starting XI was already good by bringing backup GK (Dmitrović), RB (Montiel who should become a longterm replacement for Navas), LB (Augustinsson - not playing so far yet so could be another Lopetegui "victim"), winger (Lamela to compete with Suso at RW), striker (Rafa Mir is a clear improvement over LDJ) and Delaney who can play both as a DM (to give rest to 34 yo Fernando) or in a CM rotation alongside Jordan, Raki, Oscar Rodriguez,..
I think both Monchi and Lopetegui are co-working well together which is something we haven't seen here in years if ever (on that level). Multiple SDs (or even presidents/boards) have bought players they've liked not caring what whoever our coach was at the time would think about them or if he'd possibly prefer other players who could've turned out better because he'd actually like them and stick with them even if they'd struggle early not giving up on them after a game or two.
Sure, good coaches should get the most out of all players they have but let's not pretend that likes of Pep or Klopp have never written off any player. All coaches are stubborn but in the end it's their results that will show if they have the right to demand who/what they want.
I think in Sevilla's case Monchi is smart enough to recognize his own mistakes so he doesn't insist/push Lope to play players he spend big money on if he doesn't think they're good enough. He's signing players who can bring them immediate success not like in the past when they were looking for young cheap players like Alves, developing them for years before selling for big money while also having some success with them, mostly in Europe.
They will still sell likes of Kounde and En-Nesyri for profit at some point and re-invest that money back in the team but I think they've also realized the state La Liga is currently in and they believe they can actually compete for the title so more proven players like Raki, Papu Gomez, Delaney,... brought in last year can help them better than some 20 year old kids. They will eventually need to rebuild/rejuvenate the team in a few years but that will probably be a job for Lopetegui's successor.
Probably the only downside of this current team is they don't have their own players. Navas is the only Sevilla youth product in current first team AFAIK and he's 35. They've sold Gil who was probably their best product in last years. So a big difference to times when they've had likes of Reyes, Ramos, Puerta, Capel coming through their ranks. I think they are still relatively successful in youth categories so don't know why not more of their kids have really make it to their first team in last decade.