Chen.

• Any game I will play I will top DPS, no matter what you put in my or their team.
• He should never be picked to cc anything, very true well spotted.
• He's not absolutly depended on his D, but it's extremely important that you use it well, for it will help you soak damages.
• His keg has it's merits, but it's not my first choice, again it should never be his job to bring cc, since he can't, It would be like having a healers role be a damage dealer, not the best plan.

He has sustained damage an high clearing potential, Sonya and Arthas bring some burst, where Sonya is also a terrible tank because she offers no CC, like Chen, Arthas on the other hand is some sort of Hybrid that can deal chuncks of damage and when specced properly is also a very solid tank, especially in certain comps and in certain maps.

There is loads Chen can do no other do, but it would require you to think about Chen in a less negative way and actually realise the warrior tag isn't primarily "read; champion is only designed to tank" - Again, he's not a solid main tank, so you can't have him MT. But you think his damage output is low and already consider him trash tier, so ye... I have yet to play a game where I'm either not the highest on siege damage or the highest on DPS, very much depending on how active I am in helping team.

It would be a total shame to rework Chen, it just requires people to open their minds and think about Chen and how to properly utilize him. I'm not gonna tell you how I play him or make him work, or how I feel with communication he's able to be a great asset in a team, because I strongly feel you already made up your mind about Chen and your whole post is based trying to make maintank Chen work.