Roo Returns
Skjeikspeare No More
1989 and 1990 also had Janet Jackson, Prince at the top of their game, and "young veteran" bands like RHCP, R.E.M. among many others continuing growth and momentum. You also had Madchester, alternative bands like Love and Rockets, The Church, The Cure, and XTC all putting out great releases, and that doesn't even get into hard rock and heavy metal. Neneh Cherry, LL Cool J, Biz Markie, etc. had some hit albums. Mazzy Star was an underground/college rock hit. The B-52s.I like your reasoning, but I disagree with you. That you mention the production and arrangement aspects is.. solid analysis, imho.
My memory of that era is that 1989 & 1990, though a few gems came out, were the weakest years of the 80's. Change was in the air, though at the time it felt like music was dying... Vanilla Ice, MC Hammer, and Milli Vanilli were huge... Hair metal was on it's last legs. There was a desperate need for a new direction and the albums/bands you are referencing hit at the right place at the right time. The shift you mention was already going on and the bands you mentioned were there to fill the void. Right place, right time. Nature abhors a vacuum.
The void fillers? Are you referring to Nirvana/Soundgarden/RHCP/Pearl Jam/Metallica/Smashing Pumpkins all of whom had big records come out in the summer-fall 1991 window, or the later in 1994? I'd say the 1991 gang was organic and from hard work, touring, getting better at their craft.
The bands like The Pixies and Jane's Addiction who were supposed to be the stars of the 90s both imploded with Jane's being done by late-September 1991, but The Pixies still road some of that momentum and were part of it as Trompe le Monde was released in the fall on 1991.