No. It isn't.
In fact, it has little relevance whatsoever.
When Denis Irwin was at Latics and Lee Martin was playing LB for Utd, would that mean Martin was the better of the two, just by virtue of the fact he was on the Utd books?
Amos is a 4th choice keeper who (IMO) won't make the grade without a massive amount of improvement, and Dean Brill has also come as far as he is likely to, after playing in the lower leagues for the bulk of his career.
Who is to say Amos wouldn't have been dropped twice if he'd stayed?
Neither have proved themselves any better than the other, and other than reading statistics that are (Perhaps wrongly, who knows?) loaded in favour of Brill, there is only opinion dividing the two - Thanks for yours, but I'll stick with mine.