Your premise is flawed, you are assuming that everyone can/will reach master prestige but this simply is not the case, some people have other responsibilities, take a guy I know for example he has a full-time job with lots of overtime so he can pay his mortgage and support his family, he looks after his baby and overall he gets to play CoD for at maximum an hour a week and will be lucky just to hit Lv 55.
Simply it isn't fair to punish people like this for that, which is exactly what your suggesting would do.
It wouldn't make sense in light of pro perks being got rid of. It's partly why I never got into MW2 much because I have played it substantially after release so anyone with a super perk, let alone a pro perk, will win an engagement against me, either purely or significantly, for that. In this game, that concept is being got rid of. Most of the decent stuff, for me at least, are either immediately available or shortly afterwards.
Dunno what the fuss is about PM, all it means is you've played the game a lot.
Most I see have K/Ds between about 0.80 and 1.20 with not amazing SPMs and even worse W/L ratios.
Prestige means nothing and you shouldn't get an advantage / disadvantage as a result of it.