Alves and his issues with Defending mostly came down to him just getting old.
During his prime years he was doing two things at once and did it well. but once he had gotten older he didn't have the same explosive pace he once had and with the way Lucho's system is of course he will have issues at times trying to get back and to defend.
But Lucho did find a solution to it and had Rakitic and Pique cover for him when needed and it allowed Alves to do his thing.
Yes, imo, in his prime years, Alves was able to "hold" the hole right side of our team and since Messi rarely defends, Alves more or less played against 2 players in any 442 formations (opponent's winger and a left back) all the time, and he was quite good.
About Vidal vs Roberto, we will have to see how will Vidal play defensively against better teams, especially since majority of teams will try to play through his side.
But against 80-90% teams at Camp Nou, who are not Real, Atletico, Sevilla, imo Vidal will be more than fine.
In majority of those La liga Camp Nou matches, we play all out attack the whole match, we usually win 5:0, 6:0 or 7:0, opponents rarely get into our half and even when they do attack, then those poor opponents are immediately surrounded by 2-3-4 of our defenders.
In those Camp Nou matches against midtable and bottom table teams, we can win against any team with 5:0, even with Montoya as a Rb, Roberto as a Cdm, Bartra as a Cb (and he looked like a Goat in those kind of matches), Rafinha as a key playmaker, Munir as an attacker etc.
Vidal could be really good in attacking, and we'll have to see how he defends.
And since we just play all out attack in those matches, he could be a better option than Roberto who is better in defending, but who isn't too good in attack as a Rb.
So, against mediocre La Liga teams at Camp Nou, Vidal would be my pick no1, since he offers more in attack.
On away matches, Vidal is still good enough against crappy teams.
Against good teams at home and against good teams away, it remains to be seen whether Roberto or Vidal are better options.
Further, about Lucho and Vidal vs Roberto, I am not too sure that Roberto is his pick No1, as this forum suggests.
Why?
1. in the last season, Alves was a pick No1
When Vidal started to be available, Alves was a pick no1, Vidal was a pick no2, and Roberto was a pick no3.
Lucho and Vidal had a fight then and Vidal lost his place.
But, while everything was "fine", Vidal was higher in the pecking order than Roberto (even though Roberto was good as a Rb in autumn of 2015)
2. further, in these 2 friendlies, Vidal started as a Rb in both matches.
While Roberto started as a midfielder again (Cdm) and later played as a Rb in the 2nd half.
I have mentioned this once before: people said that Vidal plays as a Rb, so that Lucho can "test" how much he can offer as a Rb.
I don't buy that story.
Lucho trains with those guys every single day for a few hours. Lucho knows Vidal for 12 Months already, and he knows pretty well from trainings and matches how much he can offer in attack and defense.
And the same can be said about Roberto as a Rb.
Further, someone mentioned that Vidal played only a few matches as a Rb at Barca and that this is why Lucho is testing him now.
But again, Roberto played only 5 full matches in total as a Rb (I have posted this one Month ago):
La liga matches last season, Roberto as a RB:
Bilbao:Barcelona 0:1 enters as a sub (Alves injured)
Barcelona:Malaga 1:0
At M:Barca 1:2
Barcelona:Valencia 1:2
Barcelona:Gijon 6:0
-- 5 La Liga matches only...
With that logic, Vidal actually played MORE matches as a RB last season than Roberto, and if someone needs a testing as a Rb, it is actually Roberto imo.
All in all, I still have faith in Vidal, at least against ALL mediocre teams.
Plus, about who'll be a starter Roberto/Vidal, I have a feeling that the race is much more close in Lucho's head than this forum thinks (people here mostly think that Roberto will be a starter).