Re-read what I said:
Equipment 2.0 Sandbox 1 had Tier 8-10 tanks with two specialised equipment slots; one was universal (eg. Survivability for heavy tanks) and one was tank-specific (eg. Mobility for the IS-7, Survivability for the Maus, etc). This concept allowed further specialisation but was rejected by the community rather overwhelmingly, because, quote, the community didn't like having tanks "shoehorned" into specific equipment setups (typically at the expense of the Holy Trinity Vents/Rammer/Vstab).
About the IS-3: Yes, it's a heavium. A medium-like heavy, with decent mobility (especially if you build into it with Turbocharger). Its armour has been power-crept. However, Improved Hardening doesn't rely on armour; it relies on tracks eating shots, and your tank having hit points (which it always does). +10% hp isn't "nothing" - just do the math. An IS-3 can get +150 hp with IH in Survivability, which brings it up to 1650. For context, at 1500 hp it takes ~3.85 shots at 390 alpha to kill it, while at 1650 hp it takes ~4,23 shots at 390 alpha; add RNG, HE splashes, lower-alpha gun hits and whatnot, and that 150 hp can really save your [edited]and allow you to keep your gun in-game much longer. It also helps you repair your tracks faster, and makes you lose your tracks a lot harder, even if you've already lost them once, which plays into techniques like reverse sidescraping and not being immobilised while doing heavium stuff.
About the M41: Of course, it can be built as a lightium/LT hunter. It's not how I would build any of my LTs, but it's doable. All I was saying is that the Scouting slot is not useless; it is anything but useless on the M41, considering its base view range, and potential of new equipment (eg by combining CVS+CO as a single example). Besides, why would an LT in any role not use even a single piece of Scouting equipment? At the very least you'll have Coated Optics on, which can still benefit ridiculously from that Scouting slot and the M41's high base view range.
As of not using the specialisation bonus, it's a more than viable choice in a lot of tanks. Most mediums still kick [edited]with Coated Optics-Gun Rammer-Vertical Stabiliser, despite none of them being Mobility equipment, and several Heavies can forego Survivability equipment as well.