Comparing the weight of the TS-E with the EF 180mm macro and possibly a new RF long macro is not correct:
- TS-E 90mm with a 2* extender has a 5.6 aperture (vs f3.5)
- No 1:1 magnification and
- No AF
The Tilt and shift mechanism adds significant weight and bulk, e.g. the TS-E 135 f4 L weighs 50% more and is 20% longer than the EF 135mm f2 L.
When you're shooting macro you usually stop down. Rarely is the maximum aperture size a significant factor though I'd agree it sometimes can be when shooting at lower magnifications. However, at lower magnifications, you do not need the tele-extender, so your maximum f-stop is f/2.8.
Also, you're confusing aperture and f-stop. Aperture is properly stated in millimeters, as the diameter of the entrance pupil. 2.8 is an f-stop, which is the ratio of focal length to aperture, and primarily of use when discussing exposure times.
Also, you've neglected my mention of the 250D or 500D closeup lenses. These make the lens's furthest ("infinity") focus 250mm and 500mm, and nearest focus far closer, about 25-30cm. That gives you .36x magnification. Adding a 25mm extension tube gets you up to 0.64x. Adding a tele-extender gets you up to 1.28x.
I don't think most people don't use AF for macro photography, instead setting the camera for the desired magnification, then moving the camera around until the focus is ideal.
Finally, I'm not proposing the TS-E 90/2.8 as a perfect substitute for a dedicated macro lens, so please stop complaining that it doesn't quite do this or that. I never SAID it does exactly the same things.