It's Ok that revenge gets charged when outnumbered, but if you are good enough to fight 1v2 and kill one of your attackers you shouldn't be able to "save" that revenge for a 1v1 fight, it should be lost if not used within 5 to 10 seconds after charged.
Yeah. It's bad enough that you hardly get revenge. You should be able to get revenge no matter what really. It happening in 1v1 scenarios is very uncommon.