GSP: December 29, 2007 November 16, 2013
Anderson: October 14, 2006 July 6, 2013
Overlap: almost 6 years, for the vast majority of both title reigns. They had YEARS to set up this fight, during which BOTH champions had established themselves as the most dominant forces of their respective divisions. Jon Jones' reign might have overlapped with Silva's for 2 years, but by the time he established himself as the Silva/GSP of his division, it was 2013 and they had very little time to set up that fight, the situations were not even close. Silva/GSP was about as perfect as things could have gone for a super fight to happen.
PED was never the main reason GSP didn't take the fight. His main reason had always been that it would take him a lot of time to adapt his body to MW. He feared being undersized, and wanted to bulk up, and you saw how that fear forced him to overeat himself so his colitis flared up. Risk takers like Fedor, Penn, Saku would have never concerned themselves with being undersized by 15 lbs.
Yes, GSP succeeded at the highest level by minimizing risks while maximizing profits, never said I disagreed. Being a huge risk taker doesn't mean being more successful. In fact people who take huge risks in this sport often fail spectacularly, as reflected in the records (and damage) of Penn and Sakuraba.
This is pure conjecture on your part. If GSP finished Silva at MW at any point during Silva's MW reign the debate between him vs. Silva would be all but over. There will always be doubters, but the pendulum would be swung much more heavily in GSP's favor. If you think GSP beating Silva at MW wouldn't have made a huge positive impact to his legacy you're delusional.