A disproportionate strength distribution most usually reflects a disproportionate approach to training, i.e. the basic lifts. I notice that you're not doing cleans, and you mention that you've been training for several years before having started this program. This means almost surely that you've been benching longer than anything else so it's not surprising that your bench would be disproportionately strong. It might be prudent for you to stop benching a while and devote some time to getting your squat and deadlift caught up. And you might as well break down and learn how to clean while your busy Doing The Right Thing.
Sore hip flexors obviously have nothing to do with lactate, and you need to read more to learn why. They always involve bad form, and you need to review the millions of videos posted on this forum to see what I've commented on about form problems, and then compare theirs to yours.