I have to agree, the two guns are completely different, even though one looks like a "mini" version of the other.
When you talk about M1A's, you need to know whether the receivers are forged or cast (and there's variation in the forged receivers too), foreign made or domestically produced, USGI parts or not, and barrel specifications -- for starters. You really need to start by comparing different M1A's within this grouping of rifles.
Saying the M1A is "way better" than the Mini-14/30 doesn't really make much sense because you have to pin down which M1A you are talking about, and the purpose for which you intend to use it.
I will say this, if someone said they were going to give me either a Polytech M1A or a Mini-30, I'd take the Polytech M1A.