Is six years a "bubble"? Sure, I think that growth will slow. That's obviously going to be true eventually. You cannot have meteoric increases year on year forever. But, again, there's no indication that it won't plateau. The boom/bust cycle of D&D seems to be broken. That's the entire point of an "evergreen" edition. Even if I'm kinda disappointed about the tepid changes we're seeing in D&Done, I cannot deny that WotC's business plan isn't massively successful. Which is kinda the opposite of incompetent.
Still one of the most popular products to date. It didn't just sell initially, it's continued to sell really, really well. And the art controversy was important for what, a week? That blew over and everyone moved on. And, again, WotC fixed the problem and responded to criticism. What's the controversy?
DM's Guild lists over 500 products for Spelljammer. Including a fantastic 20 level campaign that I'm DYING to run. My current Spelljammer campaign is doing quite well as well. So, again, what's the problem here?
People tend to think that these misteps and gaffes on the part of WotC actually matter far more than they do. I'm sorry, they really don't. Not in the longer run. The OGL debacle was barely a ripple. Hadozee or the issues with Candlekeep Mysteries (both of which I entirely agree with you about by the way)? News of the day and then entirely forgotten.
On Amazon right now, the only non-core book more popular than Spelljammer is Tasha's. I get the criticisms. I agree with most of them. I think the book should be about 20 more pages and it needs more material. But, apparently, no, it really doesn't. People don't seem to care very much. They are buying it in droves.