I certainly agree some of the early mistakes on Xbox One's design hurt Xbox sales greatly, but I do think exclusives played a big part.
While exclusives might not matter to many players, if you can play most of the good games one console has on the other that also has good exclusives....well, I think the choice is clear.
That is changing, however.
I think Sony has invested a lot in their first party studios for a reason, and I don't see them changing that path this early into the PS5's lifespan....especially, as you mention, they still can't keep them on shelves.
There's a ton of factors that keep people with one platform or the other. Sometimes they seem trivial and others important.
Some people will honestly stay PlayStation because of their Trophy collection, and feel connected to the brand through that. Others, won't want to walk away from the next Horizon, God of War, or Spider-Man. People are just attached to the brand, they may just like the controller lay-out, it's what they've always played, it's what their friends primarily play etc.
I don't really think that's true. The PS4 was outselling the Xbox One even at the very beginning of the generation when Microsoft was putting out better games than Sony. Microsoft "lost" themselves the last generation with their botched reveal.
Not to mention the fact that most people who buy consoles don't really care about the exclusives. Those sales numbers for Ratchet and Clank and Returnal seem about right to me given the amount of PS5s out there right now.
The attach rate for Ratchet and Clank is actually insanely high for a game. Something like 11% of PS5 owners own the game. No way that holds for the lifespan of the system, but even the best PS4 exclusives only have attach rate around that, and that's after multiple markdowns or being sold at less than $20 bucks in greatest hits collections or sales on PSN.
I do think exclusives still mean a fair amount to Sony (and they are the lifeblood of Nintendo). 5 of Sony's 11 best selling games were exclusives for the PS5 (Uncharted, Marvel's Spiderman, God of War, Horizon, Last of Us Remastered). X Box is hard to gauge because all exclusives are now Gamepass day of, but the only console exclusive in their top 10 was Halo reach for the last generation (they did produce PUBG and Minecraft though).