[mst]

And I don't get why someone would buy a "slow" zoom lens on FF as only lens. Quite a waste of FF, to put it mildly.

In my opinion, FF's main advantage is possible more shallow DOF especially with fast primes, and then the RP is never a good choice. But that is an entirely different discussion.

There's more to FF than DOF (even though it's a big selling point, it certainly is for me).

The 24-105 L IS is a fairly popular kit lens with any affordable Canon FF since the days of the initial 5D. And it's also a fairly popular lens among wedding photographers, at the long end, even f/4 can give you quite some background separation and nice blur (if the background isn't right behind the person you're aiming at). f/2.8 lenses often need to be stopped down at these kind of event shootings (weddings, conferences, etc.), that's even true for the 70-200 zooms.

Side note: fun to watch that the old triggers still lead to the same reactions and results here, even years later