The biggest issue with Kelvin is simply how he operates in comparison to other damage soaks.
Boldur has a shield and damage resistance(and fairly good regen, with and without his ultimate), and Montana has high damage resistance. The difference there is that they require less healing before they can back to soaking damage.
While Kelvin can soak more damage initially, perhaps, he requires a lot of attention from the support before he can get back out into the fight to continue to soak.
This forces a Miko pick, or at least Alani, to be able to heal him in a timely fashion, and then also takes more time for the support so they will have less heals for others.
A solution to improving Kelvin would be to boost his own regen through his helix. He already has a lot of options for regen, so some could just use some buffs.
At level one, his mutation health buff is stronger than his regen option. It takes almost a minute of regen at 7 h/ps to equate to 360 health which can be healed almost instantly by a support. 14 h/ps would be much more fitting.
At level four, his heal for 23% of Chomp damage is the best option already, so instead of buffing that value, instead add to it that killing a target grants health equal to full Chomp damage dealt. Most of the time Chomp kills will be on minions that only take around 300 damage so it still wouldn’t be absurd regen. Or change Chomp to heal for a certain % of damage dealt by default and leave the 23% as additional regen.
Lastly at level seven, his ability to regen 7 h/ps when near an ally or 150 over three seconds on a kill or assist. By that stage of the game, Kelvin should be around 4000 health. Both of these regen values are very low for his health at this stage of the game. At that point, 7 h/ps is nothing for his health pool and the damage he takes. Again 14 h/ps would be more appropriate if not more, especially considering it’s conditional(similar to Boldur’s 14 h/ps regen helix option with Rage), and 300 health regen over three seconds would be better for the mutation.
