In this new system, he is not a "winger winger", more of a "false winger", like Grealish...
For example, in 4-3-3 system we had following scenario:
----------Rodri----------------
---KDB----------Bernie-------
Mahrez--Haaland---Foden--
In this new system:
------Stones-------Rodri---------
Bernie------------------Grealish
--------KDB------Gundo----------
-----------Haaland----------------
Here Bernie and Grealish were used for build-up and KDB-Gundo were more concentrated on attack i.e they were nearer to the opponent's box.
Why this change was important: both Bernie and Jack have the best skills for the build-up, ball possession, dribbling and etc. But what they lack is creativity and sharpness in the final third. On the other hand, that's where Gundo and KDB are the best. So this tactical switch and exchanging duties of wingers and attacking midfielders helped the club a lot.
When Pep assessed Bernardo as a midfielder 1 or 2 years ago, he said that - "Bernardo is the player who loves to receive the ball wide and then cut inside, dribble.. do his stuff..". So that's why he didn't like him as a RCM. Then he moved him as a LCM and TBH he was doing well in terms of defensive duties, but in terms of offensive no that much.
So this new role of his in this new system - is something we were waiting for and that's the role - where we use all of his best skills and abilities.
Maybe that's why he has finally decided to renew his contract.
And not only Bernie, this tactical switch helped Jack a lot as well.