Image quality alone: 300/2.8 or 200/2

[Daniel Browning]

He says the 300 f/2.8 does better, but I didnt see if he meant wide open or at the same f/number.

I think he meant wide open (f/2 vs f/2.8).

I wouldn't have expected the 200mm to do well wide open. For astro, I think it makes sense to compare images of the same angular size, or the shorter lens has an advantage

Agreed. My idea was to take the astro measurements (where you can't get physically closer) and apply them to the OP's question (where you can get physically closer) to conclude that it's sharper.

Anyhow, the 200mm gets pretty much the same sharpness at f/2 as the 300mm does at f/2.8. I know this wasn't what the op's question was about, but I find the 200 to be the more impressive lens for this reason.

Agreed.