Kench should have less natural health
The strongest advantage of Tom Kench, is that he can absorb an unlimited amount of damage that is targeted to an ally that he's eating.
That is how Tom Kench is tanky.
He does not need to also be literally tanky, himself.
His character is a big, fat, waddling, fish monster! Shyvanna is an armor plated dragon. Kench is a big fat fish who likes to eat. They should not be identical in 1v1, or else the effects on champions he eats needs to be altered. TK has a lot of power in his abilities. That stun??? He -can- be "weak."