I don't think it's fair to call it heavyweight. It's both high and low level at the same time, which is part of its awesomeness (there are no "methods" -- only

I don't think it's fair to call it heavyweight. It's both high and low level at the same time, which is part of its awesomeness (there are no "methods" -- only messages (symbol names) so you can send objects messages (dynamic, has an overhead) or use a message to get a hard reference to a function pointer ("selector") and call that directly with no overhead (beyond a function call). So you can be nearly as dynamic as JavaScript or Python, or as performant as C without changing languages.