No one on these boards are scouts/professionals so if they say anything about a player, it is their opinion. So saying anyone on this board saying Urshela has issues with his swing, is their opinion, which if you watch on film, seems to be correct since he is not the guy who is not making this team, but with your logic is incorrect because it is an opinion. No offense man, but at least treat everyone the same.
http://www.baseball-reference.com/players/c/chiselo01.shtml
http://www.baseball-reference.com/register/player.fcgi?id=diaz--000yan
Going by the basic stat number, Lonnie has had a career in the pros with a .943 fielding percentage and a range factor of 2.55, while Diaz's career is at a .936 with a range factor of 2.4. League average is at like a .956 and 2.57 (at least according to the years Chisenhall was playing 3B) so both guys are below average in that sense.
Now that being said, multiple scouts, and many people who know baseball have said Diaz is better than his numbers, which tells me that he has more potential than his numbers show from their opinions and watching film, Diaz is potentially the better of the two defensively, now it is up to him to figure out how to put it all together.