I as well thought the TK class was very strong, being a ranker does take some time yes, but not impossible. Being able to spam infinite kicks doing 210k (as you stated) seems pretty high dmg to me I don't know any other class that can output that kind of damage infinitely.
Now before the kicks were doing
Heel Drop 800%
Roundhouse kick 500%
Counter kick 430%
Tornado kick 1000% (on cursed)
this damage was also being stacked with Fighting Chant (Skill ID# 424, iRO Name: Kihop)
It increases your ATK (2*SkillLV)% per party member on the same map.
For example, if there are 10 party members, and you have LV 5 in this skill, your ATK is increased by 100%.
party is capped at 32 or 36 people per party if I remember correctly so they are getting another extra 320 or 360% in big events like WoE and GvG making the damage even higher and impossible to tank