In fact, as long as these 20 entities are not attackers, and they have never been
As of today. But that "20" will continue to shrink until someone can control 51%. It's inevitable assuming "all things" stay the same.
Well how about this alternative: one corporation controls the trajectory of bitcoin protocol and network, and we're supposed to magically trust them with this responsibility, despite their sketchy and counter-productive behavior? *cough* Blockstream *cough*
Even if only one person "controlled" bitcoin, who is to say that they would want to run it into the ground?