Shouldn't Tanks do more damage than supports?
Namely... Tahm Kench deals waay more damage than
could dream of by assesing his abilities alone, he gets way more damage than shen for building either AP glass Cannon or Tank (both on-hit and ability).
I think Shen needs some serious assesing, maybe give him a passive on ult or W to help with his dueling like CDR, Attack Speed or MagicPen. Make it conditional/situational if you have to, just give him more power!!! He needs more power!!! All his abilities have mediocre scaling except for (ally only) ultimate. The only role he is strong at is support, and who wants to play a ninja support... No flashy abilities, and not enough CC and basic ability ally interaction.