Sorry, I don't get this argument at all.
I think it is always a good idea to start with the best player available and then if necessary, move on to lesser options.
From what I have seen of Pablo ( 2015 season and ST this year ), he is roughly replacement level at best. Shaw may be as yet "unproven" but he has been far more productive ( at least at 1st base ) and appears to be competent at 3rd.
Let's say that Shaw starts the season at 3rd and fails miserably. The team has several viable options. Even with leaving Holt out of the discussion so he can be a utility guy. There are Pablo himself, Merrero, Hernandez, and Rutledge. Even Graig!
All of those guys should be able to provide close to replacement value and performance at 3rd.
Ditching Pablo in favor of Shaw now has very little downside and may provide the team with it's best chance offensively. And from what I have seen, decent defense at 3rd.