Well, I don't know about your granny. Maybe you're underestimating her.
But you can surely see the influence a coach will have on his defense? 2 years ago Atletico were a joke. Regularly conceding 4 or 5 goals against Barca, lingering around somewhere in lower midtable. Fast forward 2 years and Miranda-Godin is the CB partnership in Europe with least goals conceded, winning La Liga and playing in a CL final. Similarly under Heynckes Dante looked like a beast. Now he looks like a clumsy oaf and Bayern are searching for a new CB. Rudi Garcia is known to have similar effects in organizing a defense. On top of that Benatia doesn't even have CL experience while Serie A is at its lowest ever point in terms of quality. They've dropped below Portugal in the coefficient rankings right now. A Juve side with Llorente leading the line, 35 year old Pirlo dictating the tempo and no wide players worth mentioning has steamrolled Serie A with 102 points but couldn't get past Galatasaray in the CL nor Benfica in the EL for the final on home soil. Barca hasn't even managed that feat in La Liga when Messi was scoring historic 91 goals in a year.
I'm not even saying Benatia is an amateur, I actually want him, but some people in this thread act like he's a sure bet to solve all of Barca's defensive problems and "just throw money at Roma" when in reality there are lots of question marks surrounding him. He could absolutely suck in a high line with 40 yards of space behind his back which is the way Barca plays. He already looked shaky against Juve last season when Juve played defensive on the counter and Roma played proactive. Roma ain't letting go of him for € 40M otherwise he'd be a City player now. If he comes for € 50M and doesn't prove to be the new messiah while relegating Bartra to the bench the
faces will be out in full force.