Well, I used this example somewhere before, but it was long ago, so hopefully it can help, though it does require watching some videos. Mostly just a few minutes of each.
If you prefer the guide version:
This monster is not 'hard' for most Monster Hunter veterans, but it is much more 'active' in Monster Hunter games, 'more action' is happening. Perfectly timed dodges, whiff punishes on its attacks, etc. By the nature of a Tab Target game, it 'becomes what you refer to'. 'Correct rotations while moving around ground hazards'. The 'Extreme' version just 'applies the Monster Hunter ruleset'. Only 3 people can fall, tanking doesn't work the same, etc.
Aaaand it's boring. Because by the nature of what a Rathalos is, you can't add more 'complex puzzle elements' if you want to represent it properly in a Tab Target game. Encounters in harder PvE content in Tab Target games require you to know and respond correctly to a massive number of mechanics, in unison. Various games have different styles (adding adds, creating area debuffs from the mob, requiring you to have and use specific items, or just spawning kill-zones that you have to dance through, or sometimes multiples of these, obviously).
That's 'what they think of to do' to make Rathalos even start to approach a 'Raid encounter'. Because otherwise it's just this (watch like 1 minute from 10:20 if not familiar with the game):
Now, that player is using a long range weapon, but the point is that once 'complexity' is encoded in 'movement and evasion', you will get a tier of player who will be able to overcome almost ANYTHING you throw at them that is physically possible to do. So what do devs do? They rightly make combat where there's stuff you can't avoid and therefore damage is taken. But these games are based on healing and mitigation too. The numbers don't work out.
I'm not saying these can't work in Ashes, I've outlined an 'Ashes Rathalos fight' before as an explanation to someone else somewhere. But that wouldn't be 'hard', just 'engaging'. It would barely become hard as other players showed up to PvP. But devs almost always find themselves thinking 'Ok this is proper hard content now, nearly no one will be able to do THIS, they'd have to play PERFECTLY'. And then someone will do it.
Full raid encounter difficulty is literally ABOUT overwhelming your players' mental stack while also threatening them with the DPS and Mitigation checks. Action games that aren't frustrating by design almost cannot threaten with the Mitigation check without being a serious pain to play for a large number of players. Not 'to win the encounter'. Just to PLAY.
If you've played Monster Hunter, I can probably successfully explain it, but if you haven't, it would be harder. Just take my main point as 'Given relatively free action ability, developers are constantly surprised by just HOW good players can be at games'. So their better bet is to design things where your ability to act freely is not the key aspect of success... and then we're back to 'might as well be Tab Target'.