I would not want DS9 to be deprived of Avery Brook's atrocious, Shatneresque acting style! For the show's stationary format, someone over-the-top leading the cast was absolutely essential. Sir Patrick Stewart was the perfect choice to show Trekkies - and, indeed, the world - that rotten acting doesn't have to be synonymous with STAR TREK ... which William Shatner and his co-stars had so firmly established. But there was no need to go past the point of making the point, by having Stewart be in absolutely everything. I'm glad he wasn't. He passed the baton to Avery and told him to "have fun with it." You couldn't ask for a better send-off, than that.
Definitely agree that they were better off with Sisko instead of Stewart, and I am glad how it ended up working out with Avery Brooks. However, since at the time DS9 was touted as a spin off of TNG, I was sort of surprised (at the time) they didn't move Riker over to DS9 as Commander/Captain. They ended up moviing Obrien over as the the TNG connection character (and alter Worf), but considering that by season 5 Riker's character was stagnating, that would have been a good way to do something with the Riker character.
Then again, like you said, DS9 really did need an over the top actor, and I don't know that Frakes would have filled that role the way the show needed. So in the end, it was best that they cast Books the way they did. Tony Todd would have been a good choice, too, but he had been too visible as Kern, so that wasn't going to happen.