I also think logia user can "change" or/and "use" the environment to their favour. Thinking about crocodile he was able to create a sandstorm. Well lets say it was produced out of his body, but then again how did he regenerate his own body after losing that much sand? He must have used the sand of the environment for his attack or to regenerate himself. The humans self regenration isn't that fast. btw he could also turn the environment into sand (= his favour).
Yeah' it is certainly overpowered, like (mostly) all logia user, but I do think it could be possible. Kizaru could turn the light of the sun into a giant laser or sth. It could take some time, but he would be able to erase a whole city/country/small island, depending on the size. If we compare it with Enels giant w.e energy ball, I do think it could be possible, he is an "Admiral" after all. But it have to take a certain time to charge the attack, not like he could use the sun light every sec. That would be truly overpowered.
About Dragon, he have to be strong, imo some1 like him can only have a logia fruit or nothing. But not a zoan or paramecia. I'm pretty sure in his case his name has nothing to do with his DF ability or are u saying he had his DF before his own name?
Note: I'm talking about Name not Title!