Are you talking about Sparking Blast, which is this game's equivalent of the Burst? That's kinda different, but I know what you mean by it cutting down potential combo lengths. Still, I still think it would be problematic if a legit combo could occur in this game with the duration letting a player call an assist as it starts, and then calling the same assist while it's going on to extend it.
Well it is also important to note that assists in this have different cooldowns. It is possible that if repeating assists in a combo is an intended mechanic then a character could have a low impact, low cooldown assist with that mechanic in mind.