Teammates are 100% EXPLICITLY your sidekick. It's actually CALLED Sidekicking, to have a teammate who is lower level than you.
There are Epic sets with pets in them, and there probably should be more, but I don't think there should be a pet in a standard Power Pool.
Customization options for ALL pets, Troller/Dominator, MM, Arachnos, Lore, and Epic, would be nice though.