Aye - the point being that most of that research was published after the Black Hole skill was a thing for Last Epoch. It does make the argument for “well, lets go flip this skill on it’s head, because the real-world decided we were wrong” a thing - but I’m not sure that’s a good enough reason to change your Fantasy Game.
When I really get down to it, (and a lot of this is opinion, so feel free to disagree with me) there are really three things that ‘deal damage’ in the real-world. Applications of Matter (kinetic energy transferring from entity to entity, via Gravity, Telekinesis, etc.), Energy (Potential Energy transfer, like Radiation, Conduction, etc), and Entropy (Applications of Time, Disintegration, and Consumption).
We can talk about the science behind what actually causes a Black Hole to harm objects and entities around it, but unless we’re thinking that the Black Hole itself is an application of the very last subpoint there, I don’t think it belongs in the Void Damage category - it’s not Hungry, it’s just Heavy. It’s Heavy enough that matter has gravity acting upon it beyond what most objects can take, and Heavy enough that Energy is disrupted around it, causing a point of Heat within a vast cold-spot in space, It might even be Heavy enough that Time gets a bit funky and stretches out (though that could be an argument for letting it Heal you, too…), but it’s not actively consuming things and converting them on purpose.
Again, most of this is opinion, and there’s a great deal of flexibility in Fantasy/SciFi genres for “what counts as The Void” - but in Last Epoch’s world, it’s a semi-sentient entity that Corrupts and Consumes worlds. By my own definition a Bacterial Infection could count as Void Damage - so I’m not trying to say there’s no room for improvement - but I’m of the opinion that Black Holes that Mages create aren’t a semi-sentient entity (not to say they never could be, just that they’re not, now…). If it helps, I always justify to myself that the Mage isn’t actually creating a true Black Hole - just opening a portal to/near one so that the Hole in Space is now affecting things in Eterra as well.
Changing where the Black Hole side of that portal is gives you a great deal of the flavor for changing Damage Types: Open in Inside the Event Horizon, and you deal Physical damage from the colocation of matter inside intense gravitational force; move part of that to the Accretion Disk, and you’re dealing Fire (addition of energy) damage as trapped energy is multi-reflecting off of the entities too close to your portal; shift a bit to the Vacuum Ring around the Black Hole, and you’ve got a portal into low-pressure low-mass space that does Cold (removal of energy) damage to things near it.
Again - this is all opinion; mine is no more correct than yours - just giving out some food-for-thought and justifying to myself why it works the way it does.