I play huge/Marathon and I still prefer food and hammers for my capital. It's not that I disagree that one needs more commerce; I suspect that what's happening is that a +1 isn't as big of a deal on huge maps as they are on normal maps (it's got nothing to do with Mara). That means that you can't just luck into the extra commerce. For example, the +1 from a river tile, while never great, is not neglible on Normal. It pretty much is for huge. The same logic applies to resources such as gold. You would need three gold resources to get the same spike in as you do (I say three times as much, but I don't really know how fast costs increase with scale).