I don't think it is as easy as saying that kizaru had a stronger fruit than enel. Both fruits are brutal, it is more of a matter of who is the more skilled user. It's not like kizaru moves at all times at the speed of light, if that was the case he would already be capable of blitzing every character in OP without anyone being able to counter. Kizaru can move at the speed of light under certain circumstances (such as when he turned fully into light and reflected against windows) but for him to actually strike he would have to do it in his physical form which in turn implies he has to use his regular speed meaning his attacks can be blocked. Enel could theoretically do something similar albeit at a slower pace.