What would be involved in rectifying electricity from a faulty car alternator?
Your point 3, it does not happen like that - if a diode for one phase fails then the other two phases still work but so poorly that the dc charge output is almost non existant. Which leads to a flat battery...

To replace the rectifier you have to get to each of the phase connections which means dismantling the alternator... Can’t be done only on the output terminal...

The voltage regulator is the part that controls the rotor current...