Hey @Schiocco!
The Forums & community.envato.com serve assets via different CDNs, so one doesn’t impact the other.
Additionally, while indeed the avatars from community.envato.com may link to the full uploaded image, the server only fetches the correct size when displaying the whole page (i.e: the avatar you’re referring to is just under 500B and took 52ms to load) 
Check out the image below (or try the inspector in Chrome > Resources (+refresh) > Img to see for yourself)
Later edit: @hogash pointed out that if cache is disabled, the full image is indeed loaded even solely for the avatar thumbnail (all 4.5mb of it). Thanks, @hogash 
That said, this should normally only be the case on initial visit, or if you’re using DevTools & manually disabled caching