Hypothetical scenario: an athlete is training to increase overall strength and explosiveness. He lifts with Upper/Lower splits and on his upper body day he finishes off with a tricep isolation exercise for two sets followed by a bicep isolation exercise for two sets. For example, Tricep Pulldowns (2x12) and Hammer Curls (2x12).
My question is why it isn't beneficial to take advantage of the fact that these are antagonist muscles and superset the lifts - basically do pulldowns, curls, rest (2x) instead of the usual pulldowns, rest (2x) and then the curls, rest (2x). Won't curls allow the tricep to most relax and rehabilitate almost like a rest phase would and same the other way around? Overall time is also saved.
I know that for main compound lifts like Bench Press and Lat Pulls there's probably too much of a drain on the CNS to effectively superset but I never understood why more people don't superset their assistance work, especially isolation exercises.