The difference is that for a wombo combo to be effective, it has to trap me directly in the middle (or in a corner somewhere). If it tags me while I'm on the edge of it, especially on open maps, then I can get out of it with minimal damage taken. Firebolt burn on the other hand is consistent. It doesn't matter if it goes off right next to me, or on the very edge of its range, it'll still hit me for max damage, and the burn will still last just as long. While burning, the sunsinger can track me by the dot numbers, and my regen timer can't start, so that's ~12 seconds where my hp is going down, and then there's more time you have to wait for regen to kick on. That is a very long time for anyone to hit and kill you. If firebolt hit me for 157 damage right away, then it wouldn't be an issue, however it's the really long lingering dot that is the problem.