Oak is very hard to kill because of this
No he's not, this is entirely a display issue.
There are two problems here, neither of which has any mechanical effect.
1) Enduring Cry is incorrectly still showing the base amount of life regened in addition to the total value (for Enduring Cry these are the same unless specific support effects are used).
2) The description on the total value incorrectly includes a % symbol. It is not being applied as a percentage.