It was explained 1000s of times that problem in all lines is linked with problems in all other lines of our team.
Defense:
-- Benatia or 2 CBs won't solve the problem if the midfield and attack won't press and cover
Midfield:
-- they don't run, create, play 1-2s, triangles, they don't press
-- but again, even if they will run, they still also need attacking line to press and run in the defensive actions, but also attackers need to run better, move better and score better in attacking actions
Attack:
-- again, they are crap currently
-- they need to score and move more
-- but also they need a better midfield than the one from the current Season
-- plus, they need a defense to concede less Goals than this Season
So, everything is connected. A world class CB or a world class RB won't solve any problems if there are no changes in the approach, tactics, discipline, running in ALL lines.
This is why it is more or less irrelevant if our RB will be Abidal or Dani Alves type. It could work in both ways, but it could be a disaster in both ways also, if other lines of our team won't work as they should.
Personally I wouldn't like a defensive RB as Bartra knowing that we currently still have "only" Messi who is playing like a 80 year old lately, Neymar who can't score, and Alexis who probably had a lucky Season. So, until we buy some different players in the midfield/attack, I wouldn't go with a defensive RB.
he could help in the defense, but I can see hundreds of new matches like against Elche and Atletico with 3 shots in the whole match (when our RB will be even less dangerous in attacking actions than the current one).
"A normal" RB would be the best. A guy who is good both in the attack to link with attackers and who is good defensively.
And then Enrique has to work with them and learn them that only one can go in the attack at the time.
Why limiting ourselves from the beginning with a Bartra type of a RB.
I would rather play Montoya, whom I don't rate too much, then any defensive minded RB.