There seems little point in having more categories in your rules than were used by real soldiers. In a tanky platoon/troop game, the TCs will want to have a pretty good idea of what enemy weapns are dangerous to them at what ranges. So, consider the armour thicknesses of German tanks in WW2. Pz IIIs and IVs were progressively up-armoured from paper-thin (15mm) armour to 30mm, then 50mm, then 70-80mm standards of frontal protection. Add in Panthers, Tigers, Elefants and Jagdtigers and you need at least a further four classes of protection — in fact, the same number of armour categories as the WRG WW2 set uses. A three-point scale probably won’t do for that.
On the other hand, if you’re an infantry platoon commander, a tank’s a tank. SPI’s “Patrol!” distinguishes onlt tanks and APCs, and the WRG’s splendid old “Infantry Action” rules use light/medium/heavy for tanks, based on their weight and the year (cutoffs are 12 and 25 tons up to 1941, 18 and 40 tons up to 1950, and 25 and 50 tones thereafter). In neither case does such a broad-brush approach seem to harm the game at all.
All the best,