How has the US/Russia/etc negotiated in good faith on effective measures
Note that they're required to negotiate in good faith on "effective measures" - when they figure out some "effective measures", then you can complain about them not negotiating "in good faith".
And just curious, what "effective measures" can you think of? Especially in light of the fact that North Korea is NOT a signatory to the NPT....
It seems that the arsenals are growing, or if shrinking, they are becoming more powerful overall as they are replaced with more modern weapons.
As to that, no, they're not actually building more powerful nukes. The delivery mechanisms are getting more accurate, so smaller nukes are as effective as big nukes were back in the day. Note that there are no multi-megaton nukes left - they've been replaced with fractional-megaton weapons with a CEP small enough that it makes no difference.
Note, by the by, that CEP is a function of the rocket (or bomber), not the nuke. And improved versions of rockets/bombers aren't limited by the NPT in any case.