By yourself, yea, it is very unlucky to run into. Yet, when storming the base, I mean that is the one of the advantages of being on home turf.
At the same time, while refilling can be fast, it does put the person refilling at a disadvantage, because you know where they are going to be standing next.
About saving up until you have enough people...well that is just teamwork.
If you have such control over the enemy base, a good way to stop this, is to have an infantry unit stand outside, but in range of the door.
This will force the doors open to allow tanks to fir inside.
Your perspective on being able to hold out might change once pedestals are added.
Be glad you can no longer access the purchase terminals from outside the buildings anymore.
I will admit we had games in the old days where it took "teamwork" to let the building die, because it was so hard for the enemy to finish us off.