I couldn't agree more + let those who have never flown try and carry on a few R bodies accompanied by sev heavy RF lenses. Then, let them take a selfie, showing the expression on their faces when the Carrier tells them "Too much weight!!" You'll have to check it. Hope they're carrying their nitro glycerin to help them through the moment.
I’ve flown many times with a 1D X and several L lenses (24-70/2.8, TS-E 17 and 24, 11-24), along with a 16” MacBook Pro and an iPad in carryon. More recently with an R3, 14-35/4, 24-105/4 and 100-500. My last trip was with an R8 instead of the pro body, but more lenses (14-35/4, 24-105/4, TS-E 17, 24/1.8, 28/2.8 and 100-400), plus 1 kg of loose Li-ion batteries (mainly for scuba dive lights). Never had an issue boarding, flights within North America and to/within Europe.
Apparently Asia is more strict, but last time I was there (over a decade ago), I carried on a gripped 5DII and multiple L lenses including the 16-35/2.8, 24-105/4, 70-200/2.8 II, TS-E 24 and 35/1.4. No issues then going to or within China, though I did choose to check the gear on the flight home (only time I’ve ever checked gear, but for that flight leg dealing with a different sort of carryon took precedence – our new 14-month old daughter we went to pick up).
Despite never having an issue with heavier gear, the M system is great for travel. Most trips I’m checking a bag, so my clothes and the tripod go in there. But on 1-2 day trips where I’m only bringing hand luggage, the an M body with the M11-22, M18-150 and M22/2 works very well.