Berni, have you tried a comparison, sending via Shipto (with a choice of carriers for the international leg, all giving bulk discounts and competing against each other for Shipito's business), vs having a similar package sent from seller direct to you, via say, Fedex?
You should try that. Then you'd know that "not all that cheap for big or heavy" is not the issue. You'll NEVER get that for cheap. The issue is not being sent bankrupt by shipping big heavy things. It's all relative.
What I really miss, is Australia's TNT. Their quotes for Shipito CA to Oz were almost always much less than any other carrier. Also their service, speed and tracking were superior. Made Fedex in particular look like clowns. So Fedex bought them out and shut them down. The company seems to have sort-of restarted in Oz (as a Fedex subsidiary?), but doesn't seem to do international freight any more.