... the Panasonic equivalent of a 70-200 2.8, the 35-100 2.8, weighs 13 oz.
That is a f/5.6 eq. lens. The closest comparison is the Olympus 35-100mm f/2.0, which is more than twice (!) the weight and the price of the equivalent 70-200/4 IS, longer, and not as good.
The m43 14-35/2 is 28-70/4 eq., and it is a heavy $2.3K monster. The overpriced Canon 24-70/4 IS looks like a bargain next to it, and it is considerably lighter and smaller, not to mention wider and better.
The aperture equivalences are only valid if you are interested in equalizing narrow depth of field.
And noise. And AOV.
Many people and most pros like a fast lens to be able to use a higher shutter speed. The DOF issue in no way affects that.
Nothing else does. If you are not shooting with a phone or a P&S, you can choose whatever speed you want.
As for the price of any lens, it is either worth it or it isn't. I would gladly pay $2500 each for the f2 Olympus lenses if they would focus quickly on an OM-D. Not only would I be able to shoot wide open at good shutter speeds in dim light but I would also have the advantage of being able to have two people in focus in the frame.
Even though those lenses are large, the comparable lens in terms of true speed will never be made for a FF body.
"True speed"? What prevents you from getting the same DOF on FF?