Zercher squat is arguably more important to strongmen than a back squat. You gonna pick up a 300lb stone with no handles by training to hold weight on your shoulders? If you wanna lift heavy awkward things from the ground you need to get used to hundreds of pounds cradled in your forearms. If your zercher squat is weak, it's because you're weak. Do it heavy and you'll get it. And for the record back squat is my favorite exercise after deadlift, but a truly strong person shouldn't be afraid to prove their strength in all kinds of lifts.