3.5 was planned before 3.0 was even released. Monte Cook wrote about it back in 2003, and the story was carried on these very boards.given how quick 3.5 appeared.
I can't find his article now (the website on which it was posted seems to be defunct), but here's a bit that was quoted on ENworld a few years back:
See, I'm going to let you in on a little secret, which might make you mad: 3.5 was planned from the beginning.
Even before 3.0 went to the printer, the business team overseeing D&D was talking about 3.5. Not surprisingly, most of the designers -- particularly the actual 3.0 team (Jonathan Tweet, Skip Williams, and I) thought this was a poor idea. Also not surprisingly, our concerns were not enough to affect the plan. The idea, they assured us, was to make a revised edition that was nothing but a cleanup of any errata that might have been found after the book's release, a clarification of issues that seemed to confuse large numbers of players, and, most likely, all new art. It was slated to come out in 2004 or 2005, to give a boost to sales at a point where -- judging historically from the sales trends of previous editions -- they probably would be slumping a bit. It wasn't to replace everyone's books, and it wouldn't raise any compatibility or conversion issues.
That doesn't invalidate your point(s), but it does change some of the underlying assumptions.