All this is true; but Nadella has driven real change at the company that was long overdue. I had been a frequent critic of Ballmer's management of the company, and I like a lot of the things that Nadella has been doing.
Ballmer had an attitude that Microsoft needed to dominate every industry they participated in or they would take their toys and go home. That mindset doesn't work in today's technology world, where markets overlap and shift rapidly.
Nadella can't change the culture of the company overnight, but he has pushed through a bunch of great changes to their product strategy -- especially in the consumer space. I mean, Office 2016 finally has a consistent interface on OS X, Windows and Android/iOS. And Microsoft has an enterprise sales partnership with Apple! That would never have happened under Ballmer -- Microsoft is essentially letting Apple use its greatest asset (its partner sales channels) to push iPads so that Microsoft can sell Office and Exchange licenses. Nevermind that its channel partners were already selling their clients iPads anyway; Ballmer would have crammed Surface down the pipeline and wondered why sales numbers were sluggish.
I think toward the end of his tenure, Ballmer started to see why the company was so dysfunctional: it was built for the cutthroat tech landscape of 1998, not the highly fractured-but-integrated market of 2015. His last major moves as CEO were to get rid of the most divisive senior executives to pave the way for a guy like Nadella who could be a peacemaker with the rest of the tech world. Ballmer tore down the silos about a year before putting Nadella in charge of rebuilding the company, which in hindsight was a great move.
All this said, you're absolutely right about keeping one eye open: Nadella is pushing change from the top, but there are a lot of middle managers and junior executives who still do things the old way and will probably never change. You can't change the culture of a company overnight, and they will still continue to be evil in lots of small, subversive ways. If the market lets them get away with being shitty to their customers, they will do it.