Remember that Riot pushes that most of their champions are viable. The pattern could be that people rediscover old champions and find their strength after popularity increases, leading to a nerf.
Doesn't explain the buffing early part, though, so I'm still suspicious. What would really help is a semi-detailed list of champion buffs corresponding with new skins for them. That way we could see the size of the buff, the amount of time before the skin, etc. Most of the threads I see like this are based on general feeling or four or five big champions without hard information. Maybe you could be the one to do that?