There are multiple reefers who keep multiple dwarf angels in one tank (as do I), and this is generally not a good idea, but they manage to do it with thoughtful aquascaping and by dividing the tank into different habitable zones.It all depends on their personality honestly. But most reviews I'm reading now say they are extremely aggressive against weaker peaceful fish.
It sounds like you've already decided to rehome the angel -- and that may in fact be the best solution -- but the angel may not have been the problem in the first place. I recommend that you set up a remote camera to watch the tank when you're not in the room. You can often uncover hidden sources of friction that you wouldn't see when you're present.
55 lbs of rock is not excessive for your build. Remember that fish are like people; not everyone enjoys living on the ground floor of an apartment building, and when you do crowd everyone into the level, conflicts will likely arise.
Macroalgae can act as wonderful tank dividers if you don't have planktivores that will eat it all. Fish are pretty visual, and conflicts will often end when the fish can no longer see their rivals.