I think the average capitalship is too small with respect to gameplay and battle graphics, thats probably just a question of personal taste though. Of course the bigger you make the ship the more detail you need to pull it off.

There are several capital ship mods, though I don't know if any of them make them larger. I do think that they are a bit underpowered though. A capital ship can be destroyed by about a dozen or two of light frigates, which is sort of lame.

Haha, I find the comparison to Freespace quite amusing, because the scale in Sins is on the exact same terms. In FS you fly in a fighter, so everything seems huge. And sure enough in Sins if you camera focus and zoom in on a single fighter, capital ships will take up most of your screen. But since you're usually always focused on frigates and cruisers (which are much bigger than the fighters in their own right), the capital ships comparatively aren't as ginormous. If instead you flew a Corvette or something in FS2, most capitals wouldn't stand out nearly as much, not counting the supercapitals like the Colossus and Sathanas.