My own experience -- MGs can (and will) be a risk to armored cars. To wit:

This from a battle conducted more than a few years ago ... not exactly the case we are discussing, but close enough in it's core components.
I was driving up a road with my little Italian L3 leading a company of infantry in trucks. I enter the town and find a French AMD-178 armored car blocking my path. I spray him with my dual MGs, and both suppress him (note the suppress marker) and immobilize him (I use black smoke emerging from under his hull to mark the mobility kill).
This gave me time to get out of the road with my soft and squishy targets, to drop some artillery on him, and to move my infantry up through the buildings for a close-assault. All of this done in quick succession, the A/C was destroyed before I could even bring up my mighty M11/39 tanks to engage with their cannons.
A perfect example of "I can't penetrate his armor with my MG, but I'll still shoot away at him just to see if I can fnck him up a bit".
But that is not to say that small arms fire can easily dominate opposing light armor. Far from it...

In that same battle my L3s went on to provide brilliant service suppressing French infantry in the first line of houses of the town. I did this by staying back, out of close-assault range, and bringing enough MGs to bear that he really had no choice but to either pull back, or watch my infantry form up and advance into lethal range. As he had no anti-armor weapons in that area he really was over matched by light armor with MGs.
Very satisfactory game play, in my experience.
-Mark
(aka: Mk 1)