Someone other than a member of the Son family more or less finished off the main villain of an arc... that's more out of the box than DBZ ever was. I'm not saying it's better, but by no means does it need to go away.
Trunks also finished off Cyborg Frieza. Though Frieza's re-appearance in Mecha form was extremely quick and short-lived...
How about letting Vegeta get a win for a change, Toei/Toriyama?