Exactly - the dynamic tier review comes with regard more to qualifying for elite tiers and moving up the ladder, so that
1) You are moving up dynamically, as and when you qualify
2) Your flights taken to qualify for Silver, still count cumulatively as you qualify for Gold, and then finally up to Platinum - this is great, because a bunch of longhauls in a premium cabin mean that within 6 months you can go from blue to plat (unlike other airlines where your tier points get set to 0 every time you move up a stage). Here they only get set to 0 with regard to retaining the tier you have attained.
3) The whole point of the multiple review criteria is actually to reward long time loyalty. Its a bit of retention discount. So for example, if there wasn't the multiple review criteria, one would have to earn 120 tier points over two years to keep qualifying for platinum.
However, at 108, after 1 year of being plat and earning 60 points, one has to only earn another 48 to hold on to platinum.
This accounts for slight up and downs in an individual's travel patterns without penalizing for not flying the exact same amount year to year.
It actually awards long term loyalty and is one of the few aspects of JP that works really well...