Biggest Blueprints’ drawback is any of you may wakeup someday and discover that your character controller BP is simply corrupted and only god knows why. Than you’ll waste some time looking for the last backup you have where Editor doesn’t crash when you try to open the blueprint and lose some extra hours reworking what you’ve done the day before.
Blueprints crashing Editor when you try to open it is not uncommon, plenty of complaints on AnswerHub.
Also there are bugs with function libraries and some other smaller annoyances. A solid scripting API where you can code while the game is running may be valuable. But Mono, hmm… I do not trust too much.