As is, deflection damage is generally deleted from CoH2. The all or nothing coin flip has caused lighter units to disappear in the late game since they can barely contribute to the foght anymore. They become pop cost inefficient compared to higher tier units. The existance of heavy armor then forces all factions to have access to high penetration units, otherwise heavies become a game ender. Those high pen units (TDs and ATGs) in turn shit on medium armor, which is why from 2v2 upwards you'll always see a Panther and Comet spam. Due to similar reasons, other units such as the StuG, JP4 and SU76 disappear from the late game: Because they might be unreliable when they need to perform against heavier armor.
As much as the current system promotes overreliance on high tier TDs, a deflection damage system would just promote spamming low tier units instead of teching, which would be bad too. I'm sure we don't want to go back to people spamming SU-76s and just frontally out DPM-ing everything. If the opponent invests in a (super)heavy tank, which comes with a lot of tech costs nowadays, you should be forced to invest in higher tier units yourself too. We've purposefully raised the costs of superheavy vehicles, so spamming low tier crap to counter these late game units rightfully shouldn't work. In this particular case, there is no way a pair of 270mp ATGs should even have the slightest chance to significantly damage a 1500mp/500fu superheavy tank from the front.
Imo deflection damage would be a bad solution. Hopefully side armor in CoH3 will help. Then low tier units can still deal damage, but it would still take effort to position them to get to the side armor, rather than just relying on sheer DPM to cause damage on frontal deflections. And high tier TDs wouldn't need such ridiculous pen values.