10k hp is fine... cuz there are champs that can deal with high hp tanks if played correctly
to name 2...
the issue is him getting FREE TRUE DAMAGE for having 10k hp so he gets to one shot anything that comes near him
let say he has 10k hp and he is max rank on feast so lvl 16 he would have a base hp of 1854 so he would have effective 8146 bonus hp
his ult at max rank is 650 true damage + 50% ap +10% bonus hp so he has no AP
650+8146x10% (814.6) so 650+815=1465 true damage to a target
let take the base hp of lucian at lvl 16 (1712hp)
so if cho was to ult him from full hp lucian would have 247 hp left just for cho walking up and hitting R
so if we take the 10% bonus hp scaling off of his R and just increase the base damage even to 1000 true damage at max rank
1712hp-1000true damage = 712 hp lucian lives