This issue of reduced vitality on HoM pets has been discussed extensively and I don’t believe we’ve received any official response.
The fact is, being a GW1 player from day 1, I would like to use my HoM pets but they are simply weaker than their equivalents. If the issue is about using 2 of the same pet in order to use the F2 skill on both swaps, the HoM skins can be made to simply replace their equivalents.
Please, I would love an official response on this issue once and for all.