There's also no reason you can't model tankettes with the current designer, either. It fits with how it works, and the designer does a good job.
I pulled up the T-27 in the game, and it's just an Interwar light tank with a heavy machine gun and armor that is almost pierced by Tier 1 infantry kits and is completely pierced by Tier 2 infantry kits. If the Soviets had a pile of these at start, it probably wouldn't be too overpowering except that we can refit older tanks.
So, let's say you gave the Soviet 2800 of these crappy vehicles. Well, I'm either sending them to China to help China against Japan (and to farm some XP for me since these are Soviet tanks and not tanks I, umm, borrowed from the Finns or Baltic states), or I'm going to refit them into something decent for about half the cost of a BT-7. Given the limited utility of light tanks anyway, either way is a solid move for the Soviets.
I mean, even with the existing smaller stockpiles, I rarely have need to produce actual new light tanks as the Soviets. I can satisfy my recon needs by refitting BT-5s. Hell, with another 2800 light tanks of whatever type in stockpile, I could afford to use light tanks as partisan suppression tools if I just felt like it.