That also isn't how it works, I'm afraid.

The black hole gets less dense because the so called "event horizon" becomes larger, the space inside doesn't stretch like we see in the universe.

It's a little removed from my area, but as I understand it there are similarities in the maths. The observable universe has a horizon in some sense, but it's not a point if no return like a black hole, so much as a point of "the universe hasn't existed long enough for anything to be able to travel that far yet"

This has a similar effect as a black hole, but it's really just a concept we see in perfectly flat empty space, light taking time to move.