No, for the love of all that is sacred, no. Kelvin gets loads of hp from Chomp. If any character doesn’t want to get +hp on gear, it is Kelvin. 280 or 210 hp is laughable when you can get 10k naturally.
You missed a helix. At CR5, he unlocks a level 2 helix that adds 3% of his current hp to his Chomp damage. Also, the 500 max damage is the maximum base damage. Skill damage multipliers and the like will all increase that (when I was mastering Kelvin, I was routinely dealing 700+ damage with Chomp because I had over 10k hp and skill damage gear).
I’m getting tired of explaining the math on this to people, but no. Boldur has enough hp that stacking hp on him is redundant. People like to bring up his current hp into bonus damage thing as if the ~80% he can get by stacking hp to get 4k hp is impressive; they completely ignore the fact that, if you stack no hp at all, he’ll still have 3500 hp and be getting 75% +dam so stacking all of that hp only really gave him a ~2.8% increase in damage (180% / 175%; attack bonuses in BB are multiplicative so a 5% increase would actually be a 5% increase).
High hp characters get more out of DR than they do out of +hp. The only characters that should be really stacking +hp are those characters with low hp because, as a static value, the flat increase to hp amounts to a significantly larger increase to their total TTK than DR would. In addition, unlike +hp, DR also acts as effective +shield, +regen, and +heal received because it allows all of those values act upon lower incoming damage amounts.
Other things to consider: +regen gear is pretty much worthless because it provides so little. The only reason to get +regen is if you’re not playing an Eldrid and want to be able to top yourself off from what little damage gets through your shield while out of combat. 7 hp/sec is pretty much nothing. At 1k hp (e.g. level 1), it’s going to take 140 second to get you back to full health from nearly dead. Furthermore, stacking more +hp to make it go up faster isn’t going to make regen any more valuable. 7 hp/sec is as bad when you have 100 hp/sec as it was when you had 100 hp/sec (in a comparative sense, its actually less valuable the more +regen you have): 7 hp/sec is bad no matter what.
TL:DR If you want a tankier tank, stack DR. If you want a sturdier squishy, stack hp. Why? Because math.