Power never was and never will be the deciding factor to any console generation. But it is very much an important part of it, hands down. People who say "power doesnt matter" are the same one's who dont have it. It happened to Xbox fans curent gen. It's happening to Sony fans with the PS5. .
It's rarely the deciding factor when purchasing a console and it'll matter even less this time because people are so much more invested in digital libraries and overall ecosystems. As long as they are close enough in power to run the same games and make them look the same it becomes much less important overall.
There are a lot of things that go into deciding who "wins" a console generation, clearly bringing in the most money is what matters to the hardware manufacturers, if they can make more money and sell fewer units they'd be just fine, those two things don't usually go together though, Sony has been making more money off of PSN alone than MS has been with it's entire xbox division for a while now.
It looks like MS is going to be pushing the subscription model even harder with next gen, we'll see if that strategy pays off since they'll be doing it from the start vs bringing it in halfway through when the "war" is already over. At the very least it may get more people to become multi console owners but they are still going to need a ton of high quality AAA exclusive content to get people to want to buy into a second ecosystem..