Simply things like pop, minimum range for AT grenades and sight changes can be made.
Things like DPS or FHP need to be comparable to base unit (mainline infantry grenadiers). So one has to set that level first and then bother with the PF, that is minor issue imo.
Actually the balance has to start from infantry units that are available before minute 1, one vs the other, (which includes grenadiers, Tommies, Penals, riflemen, Vgs and conscripts) and then fix all other units accordingly.
You are still only taking into account a single aspect of the min0-min5 engagements which is "main line infantry" (add Prostruppen to that) fighting against each other.
Drawback of builing (map presence)/weaker prior to flamer vs utility for Pio/CE.
Access to support weapon/unit play (MG42/Sniper/mortar; clowncar/sniper/mortar -not sure how to classify maxim still-; Kubel ; mortar; Vickers) vs stronger early units (Rifle/SP/IS).
You can't have comparable main line infantry performance, when they have disparity on support weapon performance, scaling, utility, AT tools, mid/late game capabilities, etc.
When factions are 1 dimensional, you need to remove from 1 side but add at the same time on another.
When factions have multiple facets, you hammer down the cheese/overperforming and you then have to raise/lower the overall bar.
And here comes the problem of scope and vaacum as well.
TL;DR: fixing non doc main line infantry is not going to fix most of the problems, when factions powerbudgets are distributed asymmetrically and not all of them "require" main line infantry in numbers to work.
PD: as you say, PF are a minor issue in the grand scheme but it's main issues can be fixed easily.