Are rep schemes like drop sets and extended sets harder on the CNS then straight sets that have the same number of total reps?
I don’t purport to be an expert on weight training but to the best of my knowledge drop sets, extended sets etc. are quite hard on the CNS. Even a straight set pushed to failure inflicts severe burden to the CNS, left alone if you extend the set past the moment of failure. Therefore, the answer to your question will be yes, they ARE taxing to the CNS.
Hope that helps.