Yeah, accessing the outernet was sort of an afterthought with i2p, although the proxies are handling well now...things got way better after stormy cloud came on the scene imo. you can stream clearnet videos through the 3 i mentioned. It could be better if there was outproxy switching built in like tor, i think. It was bad though before stormy cloud and often unusable, the available outproxies were very much overwhelmed. sometimes they worked but it was hit or miss.
that's the right line of thinking. vast majority of tor users don't contribute to the network which is held together by a comparatively small number of volunteers. by default if you're running i2p you're contributing (except with specific configurations). With tor, more users, same number of nodes means less bandwidth for everyone. With i2p more users means both sides go up, more nodes, more bandwidth, on average more bandwidth for everyone. Torrenting burns bandwidth but on average more users grows network capacity.