Perhaps. Do we need an early game light vehicle that's so resilient to small-arms fire?
It's not resilient to small arms fire, it is resilient to Volksgrenadiers small arms fire. Grenadiers damage scout cars just fine.
The reason for this is that grenadiers (like conscripts) do 16 damage per shot, and volks (like riflemen) only do 8.
If you slice the M3 scoutcars armor it would be completely useless against Ostheer as a combat unit. The M3 does not have suppression, which is the only thing that keeps kubels alive against small arms fire. Better to just apply the fix where the problem lies: the volksgrenadiers damage per shot. Just doubling the volksgrenadiers damage and cutting their accuracy in half means they will be better against scoutcars like grenadiers, but will not be better against infantry than they already are.