I'm with those who say you need to be checking up on the CNAs. You are already wasting time on answering lights, so spend that time instead of checking up on the CNAs.
IF you find they are slouching, write it up. Patient care is the number one goal.
IF you find that they are working their butts off and still not keeping up, then don't "just" answer a call light - grab a CNA and say something like, "I'll grab that call light - you go get vitals in room X." They will appreciate both the direction and the help. Do your assessments, take the next meds in, etc., while you are in with that call light. Less wasted time.
Don't just give the CNAs a list of what to do at the beginning of the shift. Know what needs to be done by them and keep on it.
Overarching all of this, *leand them, and treat your CNAs with respect and recognition for their hard work - even the ones who might not deserve it. By doing so, you can sometimes turn them into ones who Do deserve it.
Best of luck in a tough sitch!