In all honesty, it's not that bad.

Especially in lower level dungeons.

Basically, everything that isn't level 60+ is pretty easy these days and quite forgiving for new players. If anything, the biggest issue is actually trying to do something before a high level player that is sync'd down decimates everything in like 2 spells (Which, would include yourself as a RDM queuing into Sastasha )

People aren't particularly toxic in dungeons, even if people do mess up. The only notable time this isn't the case, is Reset Tuesday when you get people running duties for Challenge Logs and weekly bonuses where there can sometimes be more salt for bad play...

Though, in general, as long as you do something vaguely resembling your role (Tank stuff as a Tank, Heal stuff as a Healer and explode stuff as a DPS) people are pretty lenient.

If you're REALLY that concerned, you can head on over to Palace of the Dead and queue into Floors 1-10.

Since, much like Sastasha, you'll be level gated from your abilities (In this case, you'll start at level 1 and end up ~level 20 by the time you reach the boss on Floor 10) but unlike normal duties, roles are not a concern here, you can get 4x DPS jobs in a party or 4x Healers etc. Literally, any combination of roles you can imagine. Thus, the content is much more lenient and it's more about just going through, hitting some enemies, triggering a bunch of traps that make you feel like an idiot and eventually getting to the boss.

Also, Floors 1-10 are only done in a party by people whom are new to the content (As opposed to Floors 51-60, which can be directly accessed after unlocking instead of starting from Floor 1. Which means these floors get farmed for Experience) and thus, it's guaranteed that you'll be with a bunch of newbs who will be running about trigging a bunch of traps.