Thief stealth
Thieves have many ways to obtain stealth, but they have a cooldown on how often they can stealth. Unless they’re popping Shadow Refuge and standing in it (a welcome target for any attack since they are confined to a small circle,) they can’t stealth for longer than 3-4 seconds. The stealth cooldown also lasts about 3-4 seconds.
Thieves focusing heavily on stealth are generally foregoing a lot of raw survivability tools to have those options. Keep in mind that Thieves are not immune to damage while stealthed and performing any action besides rolling breaks stealth. Even hitting 1 near them will hurt them even though you can’t see it.
I’d suggest trying a Thief before making misinformed statements about them.