Crop sensors don't require all that glass.In principle you are right if you leave the DOF point away, but I have to correct you in some terms.
Have you seen the "ZUIKO DIGITAL ED 300mm F2.8"? In FF equivalent it is a 600 f/2.8 That's wrong as you do not take the size of the sensor into account.
If you want to gather similar amount of light and want to achive the same DOF on FF
a 600mm f/5.6 would be the equivalent.
To make a better comparison:
Take the EF 70–200 mm 1:2,8L IS II USM
If you want to have the same DOF on FT you would not need a 35-100 1:2,8
but the ZUIKO DIGITAL ED 35‑100mm 1:2.0
If you compare those two, the Canon is lighter, cheaper and even smaller.
Of course, you can take at MFT the new M.ZUIKO DIGITAL ED 40‑150mm 1:2.8 PRO.
This will be lighter, smaller and cheaper than the 70-200 but for the tradeoff of DOF and absolute light gathering on the same area (!) of the sensor.
And don't start with the "equivalent aperture", that's only for bokeh, the Zuiko is as fast as a 2.8.Of course f2.8 is physically always f2.8 but your comparison here is wrong.
Now, I know that a lot of FF fanatics ...
And of course you can take wonderful pictures with MFT.
And I am not a FF fanatic. Indeed and I am very interested in Olympus MFT system (as you probably can imagine by my knowledge about the lenses).
But your argument is physically only correct when you agree in the tradeoff of losing shallow DOF and absolute light gathering.
This you can only compensate by using lenses with bigger apertures and therefore losing the size/weight/price advantage.
No, MFT is a two times crop, you don't lose one stop of aperture you lose two stops (inverse square law, the sensor area is 1/4 the size).
If you want the same DOF you need a 35-100 f1.4 on a MFT compared to a FF 70-200 f2.8.
Nothing touches the 135 format for selective DOF control if that is important to you, further, iso takes a two stop crop factor hit when talking equivalence too.
100mm, f/1.4, 1/200, ISO 100, on a mFT (4/3) camera,
Gets an equivalent shot on a FF camera as
200mm, f/2.8, 1/200, ISO 400