In one sense it does. A big Swan No 6 nib is a glorious sight, but that’s purely aesthetic appreciation. It doesn’t really do anything more or better than a smaller nib.
In the case of a rigid nib, that expanse of gold between the tipping material and the section doesn’t really do very much. It provides an anchor point for the tipping, it covers the feed and aids capillary action. You might as well make a short, slender tube to enclose the business end of the feed and apply hardened tipping material to that. Wait a minute! Did I just reinvent the Parker 51 nib?
With a flexible nib, the metal does a bit more. It’s the springiness of the tines that enables the line variation. Again, though, large size isn’t really an advantage. One of the flexiest nibs I ever had was a Wyvern, one of the tiny ones the company was infamous for in the early fifties. The little thing would safely flex to a fishtail shape – four or five times its original width which was fine – and snap back instantly. I’ve had other, larger nibs that were as good, but none that was better.
I’d say nib size doesn’t matter except as eye-candy.
But eye-candy’s important too.