My mention of Rafa facing easier youngsters wasn't to belittle his achievements now and going forward, or to prop up Roger, but merely to point out that Roger's sharpe decline in dominance after 2009 - the year he turned 28, like Rafa - may have been quickened because Rafa had come more fully into his own and Novak and Andy were rising. Rafa really came into his own in 2008, then was injured in 2009, then was at his best in 2010. Then you had Novak's great year in 2011, and then Andy joined the true elite in 2012. In other words, as Roger entered the natural plateau phase, he was also faced with three rising young studs who were entering their primes. In a way it makes his 2012 all the more impressive - he was number one for a time, and hanging with the best in the game as they were all within their peaks.
Now we have Rafa at a similar stage of his career, at least age-wise, as Roger in 2009. Yet while Roger had a 22-23 year old Rafa and a 21-22 year old Novak and Andy to face, there are no true equivalents for Rafa, no elite younger players - only a few who seem like they could be second tier talents. He does have Novak and Andy to face, but he's grown up with them; they are his generation, his peers - like Hewitt, Roddick, Nalbandian, and even Marat Safin for Roger (it is crazy to think that Safin is only a year and a half older than Roger - he's been gone so long). But the best young players on the rise are Raonic, Dimitrov, and Nishikori. I suppose we could throw in Nishikori, Gulbis, Janowicz, etc - but they're all a step down, I think, and/or older and probably have already peaked. Vesely, Thiem, and Kyrgios are all a bit younger and have yet to sniff the top 20.
To put it another way, Raonic/Dimitrov/Nishikori won't quicken Rafa's (and Novak's and Andy's) decline as much as Rafa/Novak/Andy did for Roger. I do have hopes that as Dimitrov enters his peak, and those three enter their plateau, that he'll be on a similar level as them. But we haven't quite seen it yet, but he's close!
As an aside, as a group it seems that Roger had a wider field of very good players to face, but none as good as Novak or Andy. Rafa has fewer very good players, but more great ones to face. I haven't done a close study, though, so am not sure. But it seems that the "second tier" talent was stronger during Roger's generation, but the "first tier" talent weaker.