1. Yes we can conclude Mera's water control is better than Storm. Because Storm cannot manipulate water in a fashion like constructs or taking water out of Tank etc. The ONLY thing Storm has demonstrated that Mera hasn't done is turning water into oxygen and that's pretty much it.
2. As of RIGHT NOW Storm hasn't actually demonstrated greater control like Mera. As I have posted of Mera's feat she is able to control LARGE Volumes of Water...Storm can't (or hasn't done so yet). Also just because Clouds are made of Water Storm will have to transmute that into a large mass of Water.
As I said earlier the ONLY thing that puts Storm very skilled in this department is her making water into air. That's good feat however, Mera has more feats Storm hasn't done or replicated. So 1 feat doesn't override Mera's 3-4 feats. (Make sense) lol