It's also important to note that even in Buffy there isn't anyone who becomes a Slayer
and a werewolf or a Slayer
and a watcher. People keep to their power sources pretty exactly most of the time. The fact that those power levels aren't remotely equal doesn't cause the inter-team dynamic to collapse in zero time because it is a scripted show. If you were playing it as an RPG, you'd have to have witches, named-character vampires, werewolves, watchers, and PC demons all be roughly equal to Slayers, a concession that the show never makes.
I mean when everyone in Angel got Prestige Classes in the last (and best) season, Gunn got ranks in Lawyer while Fred got grafted to a demon goddess with the power of a Dragon Ball Z character. That worked in the show because the story did not need for characters to be remotely equivalent in power or interestingness.
Does this really work? If two abilties are broken together,
Then that means that those powers are substantially more powerful when used together than other powers used together. But if a
team has good synergy and a lot of power that's not a problem - it just means that they can fight monsters harder or whatever. If a
player has sufficiently good synergy internally then they are going to overshadow the other
players and that's going to cause tension.
Synergy has to happen, and it has to be accounted for and controlled. But synergy amongst the party members is a good thing in virtually all cases. If player A + player B together are much better than either individually, then power differences between player A and player B become hard to see. After all, when both characters do their best work together with the other, it becomes largely immaterial which of them is nominally bringing more to the table.
Thorns Aura and Skeleton Armies together is crazy awesome. And while that's going on it isn't even super important which of them is nominally "better." Both players feel that they are contributing and are grateful for the contribution of the other.
-Username17