Guards are in a good spot. For you idea to be implemented, a whole lot more would need to be tweaked and changed so that the're AI wasn't completely unreasonable as a result. The only time I have struggled when using them is when vs falls, and everything struggles against falls.
You do realise the difference in DPS between the PTRS and a guard mosin is 0.5 at long range and less than 3 point blank, right?
By the time you get your MGs and are making use of firing positions, it nearly irrelevant. It only makes guards less pinata if you don't want the PTRS, and better on the move (where they still aren't anything compared to their stationary firepower).
It would hopefully open up early game guards as a mobile flanking squad. Perhaps even something worth skipping the MGs on to use to push out weaker squads like Ostruppen or AT pfusis.