People are getting too wrapped up into the semantics of things. P4P is mythical at best. It's really as simple as "who is the best fighter taking all factors into consideration regardless of weight class. It isn't who beat who previously, or who would beat who in a match. It is who is the best fighter period. Typically this is based on:
1. level of opposition
2. number of weight classes conquored or competed in
3. length of reign
4. skills-how fights are won
6. mental toughness
JBJ is definitely tearing through the scene and winning in amazing fashion. He's very unorthodox and doesn't seem to have a challenge in sight. Anyone can make a solid argument for him being the p4p best fighter in MMA. The only real ding against him is that Silva has done what he has done and had quite a long reign doing so. Sometimes people just can't sustain a reign at the top. Injuries, losing mental focus, etc can take the best athlete and take them out of p4p contention.
The fact Silva still competes at this level and still surprisingly has the reflexes he does is amazing. Silva's reign will likely end sooner than later just based on the fact he is a reflex fighter and those are the first attributes to go followed by speed/footwork then power. Either way, it has been amazing to watch Silva's reign and it's nice to know there is a new "bad boy in town." The torch looks like it will be passed to JBJ. While he may indeed be the BETTER fighter than Silva, that torch can't be passed yet when the guy is still dominating top level opposition, hasn't done anything to lose the "mythical title."
Kinda like in boxing where you have a fighter like RJJ who was the "p4p king" of the 1990s and early 2000s. FMJ was undefeated and beating fresher and tougher competition but didn't really take the thrown until it was passed down. Andre Ward is undefeated, beating tougher competition in a stacked division and has put himself in the top 3-5. Unfortunately for him, FMJ has done nothing to lose the crown. He still has the skills and ability to beat the top level fighters he faces.
I'm not a big fan of the mythical p4p rankings and enjoy looking at the best fighters and each division and enjoying them for exactly what they are worth. Fortunately Silva, GSP and Silva are active and still taking on the best challenges and rising to the occassion to win!