People keep saying this, but I'm not seeing it. At least in modern CRPGs.
You're not seeing what? Arenas? Most recently I've seen it in Oblivion, FO3, FO:NV, Underrail, and Blackguards. I'm sure there were others I've forgotten, mostly because I avoid them. Perhaps surprisingly there wasn't one in Skyrim. If you just enjoy playing games for endless battles, I suppose arenas would be enjoyable. But to me they're a tired cliché.