That's kinda what I was saying; but I see your point, the thing is to know what "low Cp, as in amount" is the breaking point. Normally you would be shooting for Envenom uptime (specially with Kingsbane), then we have Surge of Toxins + EP. Now imagine EP does not exist, what would be the threshold then? ~40% crit makes Envenom uptime kinda trivial with some pooling, Surge of Toxins is a bit trickier but gets overshadowed by EP's dps boost.
Thing is, if 1-2 CP finishers (granting 100% Ep uptime) would be viable, everyone would be doing that, taking all the fun from the spec. Same would be if you could mantain 100% uptime using 6 CP finishers just as easily, no real fun nor sense of accomplishment whatsoever. So we usually decide to max uptime during cd's and juggle 4-6 CP finsishers otherwise (or less depending on what's happening).