The lens can be much less significant though, if you're happy with a smaller lens.
Compact Camera Meter
Compare unlimited number of cameras with lenses, see how compact or bulky a camera is and sort by height, width, depth and weight.camerasize.com
Much more significant if you're not
Not many people are going to weigh in that sort of cash for a camera to only use it with a small relatively slow prime
Well I did and the image quality an A7 and a small relatively slow prime like a 35mm f2.8 gives will easily exceed that of a MFT camera and 17mm f1.8 and the costs of a FF set up could well not be discouragingly over expensive as MFT is hardly a cheap system these days.
If you have a SLR style MFT camera and fit any lens to it it's a size and weight which needs to be in a bag rather than a pocket and once you're taking a bag the additional difference in bulk and weight of a fairly compact FF body and lens is IMO not all that significant.
I mostly use prime lenses in the 17 to 85mm range and also have a 28-70mm kit zoom and any of my lenses on my Sony A7 makes for a combination that isn't significantly bigger than the last MFT SLR style camera I had, a Panasonic G7. This is why I no longer have MFT SLR style cameras, because unless you're using lenses that tend to be a lot bigger on FF like long lenses or some of the heftier wides or primes there's no real significant advantage for MFT over a smaller FF camera. Even the MFT RF style cameras are really only a grip and EVF hump smaller than my A7 which is why my MFT kit hardly gets used these days except when I want to use my 100-400mm lens or want to shoot with a silent shutter.
I think for wildlife users the size difference is considerable, and looking at the Oly thread there's a lot of wildlife shooters posting, not necessarily saying that's the normAs is anyone who buys any of this kit from MFT and up through FF.
The point is that a small FF camera need not be prohibitively large compared to MFT and the smaller FF systems demonstrate that. Only a minority would argue otherwise and those using larger lenses which would make a more significant difference are a minority within the interchangeable lens camera minority. Some people even think that these cameras need to be bigger.
As is anyone who buys any of this kit from MFT and up through FF.
The point is that a small FF camera need not be prohibitively large compared to MFT and the smaller FF systems demonstrate that. Only a minority would argue otherwise and those using larger lenses which would make a more significant difference are a minority within the interchangeable lens camera minority. Some people even think that these cameras need to be bigger.