My understanding is that summoning is tied to current danger level, yes.

That said, lich kings in greater vaults are extremely leveled monsters anyway (as it, their experience level is far above the danger level of the area or the danger level of the monster), so having them able to summon the most powerful monsters doesn't seem like too much of a stretch to me.

Where it gets a bit more bizarre is that, say, a black wizard can do the same thing (though with recent changes, they won't appear in high DL areas anymore, so this point is kind of moot).

I'm getting the impression that balors on D:50 summon mostly kobolds, cats, rats etc, while emperor liches in GUVs can very well summon greater molochs, great karmic wyrms, ancient karmic dragons, ghost kings and what not.
I don't think that this should be the case; since pre21 is going to have summoners and monsters throughout CoC reworked, it would be nice if emp lich summons were toned down a little and balor summons upgraded.
This would make sense considering that D:50 is the final challenge for 95% of characters and the game ends here. I often have plenty of resources left after dealing with the denizens of D:50 but there is nothing left to kill.
Of course this may be the case with me since I'm a packrat, but somehow, no amount of good offensive weapons/projectiles or spells is going to be too much for a GUV.
Vaults may be skipped entirely or done at level 50 just because it's possible/easier now than before closing the gate.
Some of my chars however, skipped GUVs in some games entirely, not because the monsters inside are so powerful/tough or whatever, but because being swamped with dozens of equally powerful summons that drop no items isn't my definition of fun.

I like the current randomness in this regard. Maybe a chance (proportional to DL difference between summoner and the summoned) that the new monsters could be hostile to whoever brought them here could be better.

As I understand, both creature generation and summoning are going to be changed in p21 already, so perhaps we should first see how that will work out.

Hopefully balors will stop summoning kobolds, because that is silly indeed.

I've seen balors summon greater karmic wyrms and doppleganger kings before. I think it's random. It's just that balors rarely summon compared to a dozen liches.

I also feel the way it is currently is ideal. A PC in a high danger level area should, well, be in high danger.

We are talking Lich kings and emperors here, not kobold shamans.

All summons should be of the same danger level of the current level.

Also of note is the Master Summoner who will at times summon Giant Bats or Kobolds. Perhaps change it such that he only summons monsters of an appropriate difficulty level. Not Doppelganger Kings every time, but he shouldn't ever summon Orcs (I think).