About IFVs proactively engaging enemy's MBTs, it is usually done by specialized IFVs only.
To effectively and with some chance of survival engage an MBT, you need to have at hand a suitable cover.
Usually, in any mechanized infantry unit, some IFVs are tasked both with fire support and MBT's hunting roles: those are the IFVs that are likely to engage enemy's MBTs trying either to accomplish a mission kill or to fix them until better suited weapons take them out.
About ATGM, usually they travel at relatively slow speeds: a HOT or a TOW missile, traveling at 300 m/s, gives an MBT at just 2 km around six seconds to return fire, and even an HEAT travels at four times that speed.
Fire and forget missiles, like Javelin and Spike, have quite dramatically changed the risks, still a suitable cover is needed to avoid counter fire, and IFVs trying to deliver their own infantry usually do not take to have that suitable cover at hand for granted.
So, the choice to have most of the electronics protected by relatively thin armour, while having most vital items very heavily protected without reaching enormous masses, makes perfect sense.
In the worst case, a small caliber autocannon will accomplish a mission kill, but the slightest wrong decision by an IFV's commander will lead to the loss of the IFV, its three men crew and more or less all of the infantrymen onboard.
In the best case, such engagement will only destroy or damage some sensors without hampering the MBT's ability to continue its mission, but if confronted by enemy's MBTs the Armata will offer a relatively small and heavily armoured target while most of the enemy's silhouette will make a useful target to kill the crew.
The real point is what are the electronics hosted in the outer part of the turret.
f they are not mission critical, their loss will result in a reduction of the MBT's efficiency but without making a mission's kill.