When people were suggesting making it restricted to the shores, I had to concede it was more realistic. I didn't think Firaxis would do it, just because it is a big restriction. In the end, I think it slows expansion but doesn't kill it. Naval ships aren't spectacular to begin with. I'd probably build one or two depending on how many coasts I have to defend and that's about it. Kill some barbs with it.
Still, if I go to war, it'll be more effective attacking cities than the Hwach'a.
The question isn't if, by itself, it's bad, it's if everything else makes up for it. I'll explore with units instead. They're slower, but it'll be fine.