No one IMO is saying that RG3 has been anything short of incredible and certainly at this point better than Tannehill (even stripping out their respective offensive arsenal of weapons).
However, since hindsight is always 20/20, and essentially, taking a "mulligan" is the point of the article, an argument indeed can be made that considering RG3's 2 concussions and 2 ACL tears since '09, and factoring in the high cost of 3 firsts and a second to acquire him, knowing what we know now, for taking Tannehill before him. The issue with RG3 is that the mobility that makes him dynamic and effective is exactly what also causes him to be fragile. Can he be a great pocket passer? All evidence points toward that possibility - however, it makes him a different QB entirely. The high cost of acquisition, the history of fragility in both college and now pronounced in the hard hitting pros IMO make for a persuasive tipping point that now the benefit of hindsight regarding both RG3 and RT17, Tannehill would be the better top 10 pick on a fantasy re-do