The Fujifilm GF63 f/2.8 R WR (50mm effective) prime lens weighs 405 grams and takes a 62mm filter. The Nikon Z 50mm f/1.4 weighs 420 grams and takes a 62mm filter.

As far as I'm concerned, the primes aren't particularly larger or heavier for MF than they are for FF, it's more that the higher resolution and larger sensor size creates physical limits that makes everything slower on MF. No 20fps burst shots in RAW at full resolution with a Fuji GFX100 II, it's only 5fps. That lack of speed is reflected everywhere, because it's doing it on a sensor that's twice the size and twice the resolution, but otherwise it seemed like a pretty amazing camera to me. Speed for me is important though, so I stuck with a Nikon Z8.

In my experience on FF 40-60mm primes are always the lightest, the smallest, and the brightest (and unfortunately for me I tend to like these focal lengths the least). For comparison, Sony’s 50mm f2.8 FE weights 235 grams and costs less than $700, and I recall seeing various manual pancake lenses that are probably lighter and much smaller.

It sounds like an MF setup with say a 28mm and a 100mm equivalent lens would require more work but possible (though maybe not enjoyable) to casually carry around.

When shooting raw stills I don’t particularly care about speed. I do enjoy shooting raw CinemaDNG video, there are reasonably priced FF bodies that support it, but if I get a camera for high-quality stills FPS wouldn’t really be a deal-breaker for my uses (I guess it might for bird watching or for sports).