So what? That's the turret of the T-90A, against 3BM42. (which is 800 instead of 850 BTW) Against munitions like 125III the numbers are likely below 750. Meanwhile the CE equivalent of 90A is roughly 1000. So yeah ATGMs need more penetration to defeat tanks.The Israeli Lahat ATGM which fits in their 105mm gun can penetrate about 800mm RHA after the first layer of ERA is blown.
The penetration numbers I've seen for 105mm APFSDS are around the 600mm range RHA, including ones that use DU.
The T-90's armor on its front can reach the equivalent of 850mm RHA based on kinetic energy.
Now you've been talking about gun-launched top-attack fire-and-forget ATGMs for quite a while, can you name one of these?