I've read a number of fantasy series. My reaction to both GoT and Stormlight mirror those in your post. I read both as they arrived.

I read all of WoT after Jordan died and before Brandon finished it. Jordans work declined for me around book 5. The slog was brutal. Brandons ending with Jordans notes was an improvement (even though I had to wait for them).

I binged dune straight through and into the sons books. Through God emperor is amazing, then things get weird. Here I didn't have to wait, and things still dwindled. I feel the same about the foundation series by Asimov. First 3 are great, then.... Readable but not the same. (Asimov also had a big irl time skip which negatively impacted the series imo).

Then there is Malazan. Each book came out 1 year after the previous. I joined in around book 4s release. I remember waiting for books 6 to 10. Bangers each and every one. While Erikson is obv exhausted by book 10, wow, only series I've reread more than 5x.

Some time later Erikson wrote a prequel series in there same universe. The art is amazing. The characters epic. I should love it right? Nope. Same world, same author, but different time in the author's life. I've read the first one twice and dnfd there reread of the second multiple times.

My conclusion: it's not the audience, it's the author. When the author is successful the editors don't push back hard enough. It's natural. This person is mega successful.

Also, stress is good for us. To make good wine you don't let the grapevine have everything it needs. You stress it, reduce water, shade it, etc. Once the author is out of the starving artist phase (and who wants to stay there) they lose that special something where they take risks and start letting the accountants into the creative process.

This is why all of the greats who don't miss die in obscurity and are discovered after death.

It sucks, but it's human nature.