Arthas is not really a true tank at the moment. He is a popular pick on Haunted Mines because he has a strong early game similar to Kerrigan but he can easily fall off. If he is solo tanking he can often times have a hard time because he has no real gap closer outside of his W skillshot and his HP pool is lacking. He can work in compositions but he needs to be played a bit differently than most tanks. Generally he shouldn't be in lane early game he should be constantly rotating lanes. His Sindragosa ult is pretty flexible and arguabally better than Ghouls at the moment for strong engage and disengage. But that also makes him give up a ton of survivability so you should really run a 2 tank composition if you run Sindragosa and treat Arthas more as the ganker and bruiser (possibly use his D build in this case.) I have a soft spot in my heart for Arthas because I like his kit and he was my most played hero when he was blatantly OP but not so much anymore.
ETC has his issues at the moment as well but is a better tank than Arthas. ETC's balls got removed a few patches ago so now his damage is absolutely pathetic. He is really only existence to Q people and then eventually Mosh. Because his damage was so cut going Stage Dive isn't very viable at the moment because he dives in and then can't really do much anyways. He isn't bad but there are better warriors such as Muradin, Johanna or Tyrael.
Stitches is a niche pick and feast or famine on landing hooks and having your team know how to handle the hooked target. He isn't really a tank because of his HP pool. His self sustain is decent at best. He just isn't a very good hero to fit into most comps unlike a Muradin or Johanna.
