No, Loki is not High 3-A Universe Level durability.
It is both true that (1) no known real world force can resist a real black hole, and that (2) no real black hole has destroyed our real universe.
I scale MCU Loki to what the onscreen black hole in Thor 1 actually did -- suck in dozens of stars quickly, each of which were light years away. That would be 4-A Multi-Solar-System Level durability, and in range of the 3-C Galaxy Level MCU Thor the CRT will apparently aim for with Phase 4 feats alone.
Of course my view is that they both have always been those higher tiers. But I began this line of thought yesterday focusing on the Phase 4 Alioth feat, which VSBattles calls Hax and so I now understand does not affect tiering.
Regarding scaling to characters Loki has fought, I don't think durability should work that way. Character A's ability to survive / avoid death should not equate the Character B's ability to hurt Character A. Hurting is not killing. Valkyrie, Hulk, Hawkeye, Captain America, etc. did not kill Loki. Only Thanos did.
As for that black hole page on VSBattles, I do not understand how it acknowledges the energy-mass problem for durability but ignores it for speed characters. The logic does not hold up. Nothing real can move faster than light speed, period. Yet Flash does, and his feats are allowed here. Therefore, black hole feats should be allowed here. Seems like a big inconsistency.