We know pretty well by now that both M1 and leopard 2(before C tech) were designed against 115mm steel rod. Which is remarkably bad.Last time I checked the details were still classified. Warthunder is not a reliable source
(to be fair, their CE protection is way more significant).
Whatever the case, it isn't the most important spec for the tank in the first place - for some psychological reason general public simply treats it as one.