eye of hinokota mini boss heals too much and too often

The first randomized boss in the "eye of hinokota" heals for roughly three times what I can dish out.

I'm over leveled for the area and this is my second playthrough, yet as soon as it performs a chest pump it heals for all of its missing health for the next ten seconds, and it performs this ability every fifteen seconds, I haven't been able to reduce it's health bellow eighty percent.