This might interest you lot, David Thorpe on equivalence, f1.2 lenses and big v small...
http://m43blog.dthorpe.net/2018/06/14/big-and-bad-little-and-good/
I can see where he's going and to a large extent I agree.
Personally I do tend to use my MFT kit so that it gives a similar look to what I'd get with FF. With MFT I tend to take pictures from wide open to f4 or f5.6 or so and with FF I tend to use f4 or 5 to f8 or 10 or so, give or take, and take fewer pictures at f1.x to 4 or smaller than f10 to 22. So, mostly I can get about the same look I'd get from FF from MFT by applying the crop factor to the aperture and this gives advantages such as helping to keep the shutter speed up and/or the ISO down and hopefully keeping the image quality up too. Thankfully all of my MFT are useable from wide open whereas some FF lenses are relatively poor wide open and need stopping down a bit.
I doubt I'll be buying a f1.2 lens partly because of the cost and partly because of the bulk and weight too and partly because I'm happy enough with the smaller and lighter f1.8 primes and I'm not chasing thinner depth. I can see the appeal of these f1.2 lenses though and although mounting one on a MFT camera may take you nearer FF bulk and weight the option to use the smaller f1.8 lenses is still there. There's room for all, choice is good etc.
Anyway, it's there if anyone wants to read it.