Agreed. I've seen a few severums that were real jerks.I would be wary in regards to aggression between the sev and the angel. Sevs comes with individual personalities, so some can be punks..... particularly when they hit a certain maturity level. Due to its shape, an angel fish could be viewed as another sev.
I persoanlly would add more angels. They're not psychopaths like other cichlids. They may have little "fights" but nothing serious.