I'm very grateful that they took the time to build a native Steam Deck release for the game, not really something I had ever expected. Hopefully with this I can actually jump in and enjoy the game!
This is the reason why I don't believe when people say that it runs great without trying it myself.
I think you kinda hit the nail on the head, but I believe there is an extra dimension to this: desire.
For BG3, it looked fun and I had good memories of BG2 so I was interested in playing it. After tuning the settings a bunch and not being able to get a consistent framerate / not have micro-freezing, I just said "oh well, I'll play it on some other platform in the future." I cared about BG3, but not that much.
This is in contrast to Elden Ring Nightreign, which also had issues. I was able to get it to a somewhat stable 30FPS and celebrated that success before dumping 100+ hours into the game. Why? Well, because I love FromSoft games! I really really really wanted to play the game and was willing to put up with a somewhat subpar experience in order to get it. BG3, among other games, is just not that exciting for me personally so my tolerance of technical hitches is very different.
... which brings us right back to this native release. Hopefully the improvements we see are enough to get me over that "hill" and actually enjoying the game. I have the update queued on my deck now so I can try it out after work.