Title? I don't need no stinkin' title.
LOL. I guess the times we've gotten to 20th the parties (one I played, one I DMed) were "pathetic". Then again the idea of a character dual wielding holy avengers or +3 everything armor related is just not quite the game we play.If the level 20 PCs are truly pathetic, I guess so!
A typical level 20 party will have either an infinite-rage Barbarian with effectively 600+ hit points, or an AC 30 Fighter or Paladin type, to tank the monster. An infinite-wildshape Druid can also tank in a pinch using eg earth elemental forms.
To kill a PC you need to take them to 0 then inflict 3 failed death saves. At level 20 this is NOT EASY, believe me! I managed it recently when an ancient spellcasting blue dragon with animate objects as a bonus action attacked the druid, who had unwisely approached it not in wildshape. It took her to 0 hp quickly, then its animated treasure hoard battered her to death before anyone could intervene. She did get Revivified after the battle by a Paladin PC though.
IME the Rune Giant I posted could be solo'd by a level 20 Barbarian - I've seen a level 19 Barbarian defeat much worse (Kainos Warbringer, an AC 27 Empyrean with 2 attacks, save or stunned on each hit) in a solo duel.
I agree, barbarians get a lot of HP, but that's what non-weapon damage is for. Don't hand out magic like candy if you don't want to deal with the consequences. I suspect it's also related to the fact that I use standard 27 point buy that I don't see quite the same issue.
Not that it matters if that is what's fun for your group. Just saying that not all 20th level PCs are unstoppable juggernauts. They're just nearly unstoppable juggernauts. Big difference.