Can you make up your mind?
Are you okay?
You rolled a 1 on reading comprehension multiple times in a row now.
You can't have fights be frustrating and unfair while still being easy but having increased challenge.
I don't know how you'd even get that idea.
Of course, a fight can be both unfair and easy.
Unfair doesn't mean that something is easy or hard. It just means that the circumstances are different for the participants, that certain parties get advantages the others don't (or disadvantages, etc.).
Unfair just means an uneven playing field.
I'm fine with unfair odds in combat - what I'm not fine with is unfair game mechanics. If that Legendary bullshit is part of 5E, then that only confirms how it is worse than previous editions...
What would work would be if the player also gets maybe an extra turn and an "ignore this result" once per combat or so. That way, the mechanic would at least exist for the player as well, the boss would "only" get more of it. I'd prefer no shenanigans like that at all, of course, I'm just showing how they did the worst design possible.
I also never said the boss fights were easy.
You said that.
I think the boss fights are fine, difficulty wise. Well, the ones that I played before the rest of the game bored me too much.
No game should be designed to be hard only for people who know the ruleset inside out or are veterans of the genre - that would be idiotic (at least if it was the only available difficulty).
Difficulty is also a scale. So something can absolutely be easy and have increased challenge at the same time. Increased challenge only means higher challenge than something that is (even) easier.
So even you should actually agree that boss fights have an increased challenge in the game.
Feels like the game should have a hard setting where instead of adding HP or damage to monsters it should just double the monster count in each fight.
Usually, I'd agree with the idea, but only if they also had speed-up options.
To double the amount of waiting in a game that already wastes way too much of your time? The thought alone causes me physical pain.
As it is, I could only see higher monster stats or better abilities working well. Similar to how D:OS did higher difficulties.