I don't disagree. I think his good job vs LHPs last year should have carried more weight, even though the sample size was small. So was this sample size this year.
I did not like the Hill trade, and it certainly has not worked out as planned. However, he has a .733 OPS vs LHPs (43 PAs) compared to .641 for Shaw over 100 PAs. There's no guarantee Shaw would have done better, afterall, his overall AAA OPS was just .715 in 668 PAs.
I do think an argument can be made that Shaw's initial success in MLB was a "flash" or "fluke" (especially vs LHPs), but I agree that he should have been given more time to make that determination more valid.