D&D 5E HD Based Monster Proficiency Bonus?

As the title, how much would this affect most monsters and NPCs in the MM, CR wise?

More deadly? Or even weaker? No change at all?

I mean, as an avid simulationist at heart, it particularly irked me that certain things in the 5E system were based on this floating value known as the CR. Personally I'd like to base other CR based effects such as most Conjure X spells and of course, Destroy Undead, to be based on fixed values like CR, but well, it would take even more effort to tinker around...

So what would it turn out to be if applied?

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P.S. And I actually took the time to list how many HDs each undead monster in the MM has, trying to aim for a new formula for Destroy Undead, like 1/3/6/10/15 HD or lower for cleric 5/8/11/14/17th level and so on.

The result? "Grrr... Curse you, mummy lords!"

All other undead with a CR higher than 5 had at least more HD than the Revenant, and why did they have to have that HD...

Undead Name CR HD
Crawling Claw 0 1 (immune)
Skeleton 0.25 2
Zombie 0.25 3
Shadow 0.5 3
Warhorse Skeleton 0.5 3
Ghoul 1 5
Specter 1 5
Ghast 2 8
Minotaur Skeleton 2 9
Ogre Zombie 2 9
Will-o'-Wisp 2 9
Mummy 3 9
Wight 3 6
Banshee 4 13
Flameskull 4 9
Ghost 4 10
Beholder Zombie 5 11
Revenant 5 16
Vampire Spawn 5 11
Wraith 5 9

Mummy Lord (CR16+1, 13HD; the only undead to have an equal or lower HD total than an undead of or weaker than CR 5)

Some monsters will be more dangerous, some will be weaker, and some won't change at all.

If you look at the rules for estimating CR on DMG pg 274, you'll see that hit points make up less than half of the CR equation. The hit dice are then massaged to fit the number of hit points, based on the size of the creature (which affects the hit die size) and its Constitution.

The change is unlikely to affect the CR by much however. It's only in the case of creatures where there is an increase or decrease by 3 or more to their attack bonus that you'd need to recalculate the CR. Increasing the attack bonus by 2 increases the offensive CR by 1, which increases the total CR by 0.5. Therefore, it's only in the case where the difference is at least 3 that you might have a change in CR (since there might have been a 0.5 left over in the original CR that was simply dropped).

Fair warning though, not all creatures in the MM will match the CR which that section of the DMG would indicate. As such, you'd need to reverse engineer the original creature first, note any difference in CR, and then reverse engineer the updated creature and apply the difference from the original to the new value.

EDIT:
Also note that even if the CR doesn't change, you've still made the monster weaker/stronger if its attack bonus changed. CRs are a fairly broad range of power, so not all changes will result in a change to CR, even if it makes the monster in question weaker/stronger.

Also, I'm presuming that you will work out a hit die range to use in lieu of CR for determining proficiency, and not simply substitute hit dice for CR. The latter would result in more powerful monsters, since the number of hit dice monsters have is virtually always greater than their CR (typically by a significant amount).

Most monsters will only get an extra +1 out of this. The lowest monsters probably won't benefit and there may be some high level monsters that get maybe a +2, so it's not huge.

In my 4e conversions to 5e I use monster level to get prof bonus and that is analogous to HD in 5e.