it is strongly correlated but not 1:1.
All thc isn't in the triches, but lots of it is. If that makes sense.... and that proportion can be impacted by genetics.
your %-yield will likely correlate more strongly with actual THC%. But, still not 1:1.
more potent plant, typically a bigger yield... rosin isn't 100% thc, so other oils in the plant may not have same exact mechanics, so there will still be some volatility between yield and actual %thc.