Undead thrall attribute. How does it work with the True Polymorph spell

Question

This is a follow-up to my how to get a permanent skeleton companion question. As the previous question answered a True Polymorph spell can allow a permanent zombie follower summoned using Finger of Death in conjunction with True Polymorph to make a permanent skeleton follower.

Although I was wondering how this works with the School of Necromancy's Undead Thrall feature. The Undead Thrall feature states that

Whenever you create an undead using a necromancy spell, it has additional benefits: The creature’s hit point maximum is increased by an amount equal to your wizard level. The creature adds your proficiency bonus to its weapon damage rolls.

But the problem is that the True Polymorph spell states that the

The target’s game statistics, including mental ability scores, are replaced by the statistics of the new form.

Hitpoints are even further explained

The target assumes the hit points of its new form, and when it reverts to its normal form, the creature returns to the number of hit points it had before it transformed.

So in short my question is, do the Undead Thrall Bonuses pass onto a True Polymorphed creature?

Answer 1

No, it would be a normal skeleton. True Polymorph is not a necromancy spell, so Undead Trall's benefit would not happen. It would apply to the zombie created by the initial Finger of Death, but True Polymorph would wipe out that benefit when it changed the zombie into a standard skeleton. (This is, of course, assuming the increased HP and damage didn't raise the zombie's CR and break the combo).