>Dark energy is known to make up 70% of the mass-energy of the universe, whereas black holes are a mere fraction of the ordinary matter, which constitutes less than 5% of the universe.

Is there some cosmological constraint that says dark energy compressed into a small volume would exhibit gravitational pull and therefore contribute to our measurements of black hole masses? If not then it feels like this is a weak counterargument that makes a pretty big assumption that dark energy must have the same mass-energy equivalence behaviour as regular energy from a general relativity perspective. If black holes somehow are the origin of dark energy, then surely this is driven by physics at energies far beyond our understanding from either particle physics or cosmology. In that case aren't basically all bets off in terms of what you'd expect to observe in terms of apparent black hole masses?