LT is a much more important position than FS so if you need both and have the opportunity to fill one or the other with equal talent, surely the LT position would get he priority.
I think Clady is great also and is 2 years younger than an extremely youthful Joe Thomas. But this "simply played better than Joe Thomas" perspective I did not see. I think Jake Long was even better than Clady last year. Consider he has immobile and limped arm Chad Pennington throwing and Miami had success running the ball. As opposed to extremely mobile and rocket armed Jay Cutler and an unsually lack of a running game in Denver.
Joe Thomas is widely considered the best tackle in football right now, let alone best young tackle. The pro bowl isn't the end all when it comes to a players quality, nor are stats, but Joe went to the pro bowlhis rookie year and was 2nd team all pro this year. Roos (who was this years all pro), Thomas and Long got the pro bowl nod over Clady. Thomas' stats are no worse than Clady's and his talent definitely isn't either. Marcus McNeil is also considered one of the better tackles as well and at this point should get higher consideration than Clady in this regard.
Clady's good but there are better and I've named 3 better young tackles. 25 yrs old and under is considered young to me.