Yes. And a 400 grain arrow @ 260fps will drift and drop more thana 500 grainarrow at the same velocity.

It sounded better when I said it in my head.

At any rate, what you say is true but I think still leaves the question open for discussion. The faster arrow does have the advantage in making the range estimation a little less critical. Heavier arrows have other advantages.

The fear is that a light arrow, especially with a fixed broadhead, may be less stable, end up pointed a little sideways, and get steered off line by the broadhead.

Take a ridiculous case - even those these arguments never convince anybody - throw bowlingballs at the deer, no danger of "planing", no drift, gravityon the other hand ...