As for Palpatine, well he does have almost the entirity of the dark side flowing through him, plus whilst the dark side might not be stronger, it's easier to misuse--plus I guess you could argue the dark side keeps you alive much longer, but once you're dead, you're dead. The light side on the other hand won't keep you alive longer than your allotted years, but will ensure your spirit survives.
That works for me. It gives the dark side users more of an edge during life in a way but the overall edge to the light side users. Which means Vader got the best of both worlds - more power while he was still alive, and with a last minute act of redemption a nice afterlife. Go Vader!