The Majors and high minors are full of mid to late 20 somethings that sometimes break through due to opportunity or coaching/development tweaks, in the current pitching environment that's kinda how it goes for everyone. You obviously would want to avoid being always on the losing side of those, but there's no indication that's been the Cubs' problem. We can lament that Estrada went to SD and learned a splitter, or that Hudson and Megill look great 2 organizations and years later, but counting them as preventable failures is a bit short sighted given the circumstances(options, 40 man spots, years of experience) that drive many of these decisions. Three different organizations had Leiter Jr. before he perfected his split, Merryweather couldn't miss enough bats as a Blue Jay to avoid a roster crunch, and Miller couldn't survive a crowded Mariners bullpen before jumping to the Cubs and immediately pitching even better than his mild MLB success.