Puppy Oversocialized?

Have you tried training a look at me command? I've done this with my adopted beagle.he would literally bark howl and pull like a train to meet everyone and every dog in the street so I took high value treats (none of your cheap biscuits) and when I saw someone coming gave the command look at me whilst holding the treat near to my face, once he made eye contact he got the treat.

So we started off as I saw the person/dog further away I put him in a sit, said the look at me command and rewarded several times so keeping him distracted. As the days passed and he got to understand the command we let the person/dog get closer before saying look at me and cut the amount of reward slightly, a week or two later we kept walking and said look at me as we passed and then he got the reward.

Now days he walks past almost everybody and if a dog does come up to greet he knows he may greet but not bark and if I saw walk on its time to go and he gets a treat..
Its turned a nightmare no manners dog into a well mannered dog who can still greet happly but isnt dragging me down the road to do so,

The biggest "issue" with terriers is AROUSAL. I put that in quotation marks because this only becomes problematic in pet settings. Arousal is essential for working dogs, especially hunting dogs who depend on that drive to keep their desire for the target up. They can lack in discipline and self control, whereas dogs belonging to herding groups depend much more on their self control to to be able to predict livestock and not go as far as to harm them.

Pit Bulls can go from 0-100 in the blink of an eye, this is a desirable trait with breed fanciers. I find it fascinating and amazing to watch my dog turn her craziness on the instant she sees a critter.
The American Pit Bull Terrier was created for dog on dog combat, for this reason they make a very poor breed choice for those wanting to socialize with other dogs or have them live along side livestock or other pets. So much of dog behavior is based on instinct, and just like a hound has a strong desire to follow scents or retrievers have a strong desire to retrieve, terriers often have a strong desire to kill other animals. This is why you'll see so many videos and hear so many stories of Pit Bulls breaking through fences and grabbing neighbors dogs, this still falls on the responsibility of the owner because they should know their dog and contain it properly. Dog aggression isn't bad, what is bad is when owners don't practice proper handling and management.

Another trait that terriers are famous for is their tenacity, and this is what you're seeing when your pup bites and holds. This isn't appropriate play and can take a bad turn really fast. Break stick were created specifically for these hunting breeds who bite and don't let go. Even though this hasn't turned into a full blown fight yet I would get one of these in case it ever does.

Socializing puppies is important, but when you socialize you are still working within a dogs genetic bounds. To me it sounds like your pup is 'testing the waters' and if given enough time and opportunities he will continue to go a little further each time. As important as it can be to teach a puppy to get along with other dogs, it is equally important to teach a puppy to ignore other dogs when needed.

My APBT socialized plenty and properly and still ended up DA. I added an Aussie to my family and even though they get along wonderfully they are never left alone together and I do have to intervene when things escalate.

Limited play and intervene as soon as play escalates. Absolutely get a trainer as well.
Many APBT/AST owners use the crate and rotate method, it is a little tricky at times but sometimes necessary.