There wasn't a problem with our defence tactically, it was more down to the fact our defensive players mainly had aged and thus weren't as quick as opposition, often being exposed towards the end of games when they had tired.
In particular the FB's.
Younger, thus more quicker FB's will solve this issue that opponents would often exploit.
As with the GK, we were to inconsistent with our GK so hopefully Ederson can introduce some consistency there.
A more energetic defence will decrease the risk of us being countered.
And judging from Edersons highlights reel, he is fearless and doesn't mind throwing his body around the box during corners/crosses.
As with David Silva, he was often targeted specifically by opponents, to injure him, regularly foul him and take him out if the game.
Having Bernardo will allow us to be more flexible and if Dave gets taken out we can then have another playmaker.
So yea, quicker FB's and we'll be much stronger