My floor falls so far away from the wall that I need to shim the front feet: about 5/8". The back feet are off of the floor unless I shim them.
There's a small -very small- amount of wobble if I stand in the tub facing the valve and shake laterally. Because I have access to the underside thanks to still-unfilled stud cavities and access points for lifting the tub with flat bars (per point #7 above) I've been able to experiment with shims, without shims, shimming the entire tub higher, etc. Bottom line no matter what I have a tiny amount of wobble.
After reinforcing the joists by laminating them with a double thickness of 3/4" ply (Liquid Nails & screws) and some bridging I've concluded that the floor in bathroom has some movement and that's just the way that it is. House is a frame ranch and went up in '64. No rot anywhere, but there's always felt to be a little give underfoot for the 20 years we've been in the house. As I said, the house just moves and while I don't like that it's my house and I'll be here for at least another ten years.
FWW I had a friend who is/was a journeyman plumber stop by for beers and to have a look. "Rock solid" is what he counseled, but then felt the wiggle and told me I'm OK but (a) be prepared t0 keep an eye on the caulk seam between the tub and wall (which will be tiled) and (b) support the apron with a strip of rabbeted hardwood installed under the tub apron. Caulking isn't a problem, and the strip of wood is a fail-safe and insurance against the feet doing all of the work for the next 50 years. I like better the idea of plastic shims or even thinset to a strip of wood, but my solution is TBD until I get an evening off and can tinker.