I would have to say the heirloom gear trumps the azerite gear even if it is way lower item level. Remember 3 pieces of gear is only 3 out of like 15 slots of gear so you’re not losing that much stats overall, and the exp bonus (30%) I would say more than makes up for it.
That said, I do feel that heirloom gear (something you have to work and pay for) should more closely match the ilvl of azerite gear since it is supposed to be a reward from leveling up and paying for them. I’m at level 111 now and the heirloom gear is 216 vs. the azerite’s 280.