Aftet watching this, what would you say?
Is it worth it drilling a drain hole or not?

Plenty of drain already

I meant on a new replacement door you Viking...

Yes I know.

Never seen any drainholes but why not, try?

I think that the main reason is that the front mudflap is missing. The middle door post, rear door and front of rear wing is hit by grit removing the paint allowing rust to take a grip.

So what your saying is that rust begins from outside?

Yes helped along with moisture inside mainly in the overlapping joints.

It should not need a drain hole because there should not be any water in it, until it rusts around the window, then the water can get in.

I think Viking is right, it rusts there because it is hit by more stones, and also because the paint is thinner on the edge thanks to a careless painter.
If any moisture does get into the inside of the joint, there is no paint to protect it, so take the door card off and pour some cavity wax inside, if you can take the door off and tip it around so it gets in all the seams even better.

When I open my door after its been raining, water seems to come out the bottom.

I guess this could be water running down, but it seems to come out, but who knows!

i thought that too but water sits in the window aperture , when open the water runs forward and runs down the outside to drip off the front corner.

water does get in through the clips for the ally strip.

I doubt that water has anything to do with the rust. My front driver door has a rust hole where the inside window clip is located. Water drips or run through this hole and drains out down the bottom which has no rust whatsoever.