Sure it has good coverage but coming off that relatively weak base 85 Special Attack stat, it certainly isn't going to be broken in game. Especially when there's already the powerhouses that I mentioned above. You can make the case that Ame can't release it because Ground and Flying Gyms are coming up, but it's a snowy mountain.... you're trying to tell me that there won't be Ice types on a snowy mountain? There has to be some ice types and Lapras certainly isn't among the elite Ice types so I could see it appearing in Ep13 based off that. I still have no clue if it will of course.
I also think Snorunt, Shelder ( Eh prolly to OP), Cryogonal, Walrein, Clampearl, Avalugg,and Beartic are all strong candidates to appear in the Ametrine Mountains.