It's best to think of infantry sections casualties as "hit points" - as casualty<>dead.
A 1 man section therefore may be assumed have a couple of hangers-on (wounded, shocked, or hiding) nearby who may well be able to help the one fully functional person load the LMG or RPG.
It's a game anomaly - otherwise weapons furter down the slot list (and therefore of lower oriority) would at some point never be available for the depleted section to utilise. So - the above is my rationale for that
.
So a 1 man section WILL get 1 shot opportunity for all its slots for the first shot, until it fires, moves etc, when the normal priority rules will apply, usually leaving it with the slot 1 weapon, sometimes with rifle shots if slot 2 is a class 1 weapon.
Crews and depleted sections DO have a lowered percentage chance of failing to assault. AI Crews tend to rout from the vehicle for several turns, and often rout offmap especially if the originating unit or weapon system is destroyed. having AI crew stik around to try to dance with you is rare in my experience, so presumably those ones would have had better morale than average?.
Basically you just were unlucky to lose several tanks to crews, especially as you have TI sights and should be aware of them?. Unless they asault from ambush (the assaulting unit is unspotted). An assault attempt from hidden position has a better chance, so "tripping over" previously unspotted units is less good for the vehicle target than trundling up alongside a known enemy unit.
Cheers
Andy