The M42 does NOT compete with the USF AT gun, so this is barely an argument. Even then, the USF AT gun has a 4 men crew, no AI capabilities, a significant tech cost/trade-off, a slower turn rate and no stealth. You can't just compare the 30 mp difference between their base price.
Urban Defense is the only doctrine that combines an effective light vehicle counter (M42) with Shocks, which - together with the KV2 - has made it the most prominent sov meta this patch. All other Shocktrooper doctrines have to backtech ZIS to survive the light vehicle onslaught, unless you start with T2 and want to autolose.
Urban defense is meta because canister abuse, the same way mobile defense was meta because of call-in abuse. It does not change the fact M-42 received heavy nerfs to it's AI and cost increase to the level of proper AT-gun without any buff to it's ability to scale into late game like all other AT guns have