Don’t get me wrong, full bore tank ammo does damage to light armor in reality. But it’s significantly less effective compared to CE or autocannon ammo. The excessive penetration leads to very little post-penetration damage for KE ammo, lest you are firing specially designed Penetrator Enhanced Lateral Effect (PELE-FSDS) rounds.
Currently, all KE ammo is basically able to magically transform itself into PELE when needed against very light armor but still keep the full penetration against heavy armor. This leads to players only using KE ammo in the majority of their tanks, and many never loading any CE ammo (then complaining when the select few vehicles with extremely poor armor end up surviving multiple impacts to empty areas) for appropriate threats.
IRL tests showed that high power KE ammo needs to encounter sufficient resistance to create meaningful post penetration effects. Either fill the tin can with a million holes by shooting it multiple times, or throw a bomb at it so it turns into a crater.
By the way, “no armor best armor” is misleading. It’s “no armor best survivability”. These lightly protected vehicles are performing correctly when you have difficulty instantly destroying them with excessive penetration KE ammo. The problem is how poorly implemented HE(AT/SH) is. There’s no point in using anything aside from KE when it works for 99.5% of potential threats, and the 0.5% of vehicles that prove difficult to one-shot with KE can be handled by MGs, artillery or by shooting them full of more holes with KE ammo.