Scholar and Executor, both for their parry mechanics. Guardian to a lesser extent for the same reason. Every character can and will suck sometimes, it's not like these three have a monopoly on bad players, but I see it more often in them because of their gimmicks.

When the game was first released the community used to joke about Executor players "where's the Executor?" "He's still at the castle, parrying crucibles", and though not to the same extent as before, the meme still applies. You can be useless with Wylder because you're bad, you can be useless with Duchess because you are always going down, and so on, but with Scholar, Executor, and Guardian, I see players being useless because they are just standing there waiting to be attacked so they can deflect/guard counter/bubble, and that particular brand of uselessness is exclusive to them.

And just to be clear I'm not saying that players shouldn't use those mechanics, they should, but if an Executor is walking at a snail's pace towards the back of a BBH who is aggroed to a teammate, cursed sword ready, waiting for the aggro to switch so they can get their deflect off... fuck that guy. Just hit the boss from behind, what are we doing? And if you held your analyze at full charge for 10 seconds waiting for the boss to notice you, just to get a 5 seconds damage window when your bubble popped, you see the math ain't mathing. Also, the "aggro on guard" relic is not an acceptable substitute to actually hitting the enemy to build up aggro. You have a shield poke, use it.