At the heart of the issue, I agree. Since it looks like the Mets will be playing out the string for the remainder of the season, it seems like this would be the perfect time to find out what Duda and Nieuwenhuis are made of. That said, I think you hit on the bigger issue by saying they're much more important to the team's future. Within that importance lies a delicate balance of how you bring players along and develop them. For fans like us, it always seems more gratifying to just throw the young guys out there with a sink or swim mentality. But there are a number of facets that goes into developing an every day, Major League player. The organization has a responsibility to try to put players in the best chance to succeed, and every player is different. In Duda's case, instead of him continually striking out at curve balls in the dirt at the Major League level (which isn't good for anyone), a chance to tweak his mechanics and/or his approach outside of the day-in, day-out fan and media spotlight, while gaining some extra confidence, may do him a world of good in the long run.
Here's the thing: Bay and Torres are stop gaps. Torres was always designed to be, and Bay played himself into that distinction. And while it's easy to look at the situation through the lens of Bay and Torres taking away opportunities from younger players like Nieuwenhuis and Duda, I don't necessarily think that's the case. The organization knows that they need to find out if they have long-term pieces in Duda and Nieuwnehuis, or they have to look elsewhere. I do think once the Mets are comfortable with their progress (and Kirk needs to get healthy as well), they'll be up and getting plenty of time.