The new stuff doesn't weigh a lot. It's not FF bricks any more. Nikon stuff is mostly magnesium and plastic.
I’ve been considering a m43 for that reason.
But, be that is it may, take a look around you. How many people do you see on any given day taking pictures with actual cameras, whatever the format? I live in Paris, a city flooded with tourists, whom you'd expect to be more likely to put up with carrying a somewhat inconvenient camera in exchange for better pictures. I can count on the fingers of one hand the people I've seen taking pictures with actual cameras in the last few months. And I walk or bike to/from work, along one of the most picturesque parts of the city. However, you can see people taking pictures with their phones all day, everyday.
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[0] Some of the bodies are actually surprisingly small. A sony A7C2 is "only" twice as thick as my Pen-F, the other dimensions being similar. But the body itself is useless without a lens. And while wide-angle offerings seem somewhat similar (though there's no equivalent to the 8-25/4), the tele end is much larger, even comparing a variable aperture to a fixed f/4 offering from Olympus. And primes are an absolute joke if size matters.
IME this only lasts up to the point they have to lug that brick with them.
Don't get me wrong, I'm firmly in the "my 8 yo m4/3 kit wipes the floor with any phone it's not even funny". Which is all the more the case for a modern FF kit. But even my tiny Olympus is huge compared to my iPhone. Only my winter coat with fat pockets can fit it. It otherwise needs an actual bag (might work with some women's purses, I don't usually carry anything at all).
Guess which one I have 100% of the time with me? I've found that the iPhone in hand while outside takes 100% better pictures than the Olympus kit in the drawer at home.
It's always a question of compromise. Before my Olympus gear, I used to love my FF Canon gear. Built like tanks. Until it got old carrying all that junk around, and it started gathering dust somewhere. Now I'm happy with m4/3 when I'm relatively serious about my photography, and I'm happy enough with what my iPhone produces when I only feel like having a pair of jeans and a shirt on.
Would a new Sony something-or-other wipe the floor with the Olympus? Possibly. Enough for me to lug it around? No way.