What are the hidden subgroups in roles in Heroes of the Storm?

I thought that Quick Match would try to match you against another team with a similar composition. For example, if one team gets [1 support + 1 warrior + 3 assassins] the other team would also get such a composition.

However, in one of his videos, MFPallytime mentions that the reworked Tyrande (still Support) will be matched against another "sustain" heroes, which could even mean he'd be "mirrored" in the other team by an Abathur (a Specialist), or a Medivh (also a Specialist).

My own recent experience seems to support the hypothesis that there is such a different, more fine-grained grouping of heroes that is used to create "mirror-ish" matchups in Quick Match.

Is this correct, and if so: what are the hidden groups and what heroes do they contain?

The updated quickplay matchmaking roles are described here. The names I'm using aren't official.

Healer - The game tries to prevent 1-2 healers teams from going up against 0 healer team. Any "Support" hero that isn't in the Sustain group goes in this group.

Sustain - Again, the game tries to mirror the amount of Sustain heroes on each side. The heroes in this group are Abathur, Tyrande, Tassadar, Zarya and Medivh.

Tank - Also mirrored. Contains all warriors except Zarya, D.Va and Sonya. Currently includes Varian, but I think this has been changed twice already, and might change again.

Bruiser - Not mirrored. Might not do anything actually. Includes Sonya, D.Va, Ragnaros and Thrall. Ref

Stealth - Not mirrored. Teams are limited to one stealth character each, to prevent Nova/Zeratul/Valeera as your three dps. Also includes Samuro. There's a theory that Genji is also included in this, but this hasn't been confirmed.

The older rules which may or may not be still be effect are described here

No more than 3 Warriors.

No more than 4 Assassins.

No more than 2 Support.

No more than 2 Specialists.

No more than 3 Melee heroes.

I don't have details about how these two sets of rules interact with each other, or how the older ruleset might have been updated.