I suppose you're right. Initially, I didn't think the Rito resembled the Zora in any way, but the extensions from their arms do look fairly homologous. On the other hand, the Parella do look like they could be a "primitive" type of Zora, almost akin to a tadpole/frog sort of relationship.
I have nothing vested in either perspective; in fact, I'd prefer yours. I think it would be totally awesome if the Zora were evil. And I agree with you about the Lanayru province. I still think we're going to see Lake Hylia there.
On the other hand, I do get a "Zora's Domain" vibe from Lake Floria, and if you go by the
OoT map, Zora's Domain is adjacent to the forest. In both
TP and
OoT, Lake Hylia is located near the desert, and I expect this to be the case in
SS as well (the desert is obviously located in the province we haven't seen, I'm betting Lake Hylia is too).
That said, we can't read too much into the geography, because while there are general trends, there are some inconsistencies as well (ironically, the location of Zora's Domain being one of the most significant). I hope we the see the "Old Kakariko" from Twilight Princess. I read a compelling theory recently (I think it was by the Big One) that proposed that the Hidden Village is not the Kakariko from
OoT, which would make sense given that the Kakariko in
OoT was near Death Mountain.