I really don't think any franchise in the game would have kept Heyward at AAA for any considerable length of time in 2010. Some undoubtedly would have kept him down for a few weeks to push back the service time clock, but we had a massive hole in right field, a competitive team on the verge of a playoff berth and Heyward had just finished clobbering the holy hell out of AA. Maybe 15 or 20 years ago he would have spent some time in AAA, but in the MLB of 2010, that guy plays in the big leagues.
Simmons is a different, slightly more difficult case, and he was undoubtedly rushed a bit. But again, the big league club was in the middle of a 94-win season and spent the season in a legitimate race for the division despite a massive sucking chest wound at shortstop. I'm not going to say that we would have missed the playoffs without Simmons- we ended up winning the Wild Card by six games, and no one is that good. But contending teams just don't run Tyler Pastornicky, Paul Janish and a game but out of position Martin Prado at shortstop.