Unfortunately you'd get the opposite issue where people would hate running Prae over Castrum if they gave equal EXp since Prae is longer. Not saying that they perhaps couldn't be tightened up in terms of balance with exp to time spent, but they won't ever be the same amount of exp.

Also I dunno why people are actively calling for it to be turned into a solo instance. That might be the best thing for new players, but as far as veterans go you could simply not run it if you don't wanna spend the time. Dunno why you'd call for a source of exp to be removed.