...does a player's rating during a match have any relevance to how good they are, or is it a completely independent score?

I mean, if Lionel Messi is playing at 6.6 and some player from Dagenham & Redbridge is given a 7, is the D&R player playing BETTER than Messi... or, as he's so much of a better player, does it just mean that Messi is only having an average game by his standards, but he's still playing better than most.

Does that make any sense? It's been troubling me for a while now...!