I don't feel you are overprotective. It is your responsibility to ensure the safety of your dog and if other owners allow their dogs to snap and corner dogs then YOU need to step in and remove your dog.
The bigger dog may not have hurt yours but it seems you gave the dogs the opportunity to resolve it and the situation only accelerated. Just like humans not everyone gets along. Maybe try posting at the dog parks or other areas that accept flyers that you are looking for a play group with other small breed dogs. Think of the friends you'll make and your pups will all enjoy the exercise at their level.
__________________  Zsa-Zsa and Eva Darling Mine |