Does Magic Guard encompass of everything that Overcoat can do? Overcoat prevents weather damage, but Magic Guard prevents indirect damage, which apparently, weather damage is part of. So would it be wrong to say Magic Guard is almost strictly better, if not strictly better than Overcoat?
It is. My Reuniclus had Magic Guard, and it did the same thing that Overcoat would have done in Sandstorms and hailstorms (Plus a heck of a lot more.) So yes, it is a lot better.