Shocker is very simple. Thug. Thats literally it.
If that's the case, maybe he should just have no characterization in the films and be there just for fight scenes, nothing wrong with that if he is not the main villain.
This why I don't like Shocker very much in the comics, its hard for me to find a reoccurring villain engaging if he is about as developed as some random mugger Spidey foils, I think if a villain is going to be reoccurring, there should be more to them then that. Its the same problem I have with Carnage, there is nothing to the character and he does the same thing over and over again, nothing about him is engaging.
Shocker as a petty criminal isn't even unique in the Spider verse, characters like Vulture, Electro and Rhino are often written as career criminals who want a big score, sure maybe Vulture and Eelctro are more interested in revenge against Spidey then Shocker is, but often are they plotting revenge against Spidey vs. just committing crimes to become rich.
Captain Cold is a way better 'career criminal" villain then Shocker is, because he has a defined personality.
I really don't get the argument of people who say everything has to be connected to the main story. Spidey fights all manner of thugs, powered and non, every day. That's just a part of his life.
But movies are not comics, if you are going spend a lot of money to make Shocker work for the movies, the film makers want some bang for their bucks.
I also think from a film making standpoint, Shocker showing up randomly and serving no purpose, could throw off the pacing of the film and audiences could just become bored with it, especially if Shocker has no characterization. If Shocker is not working for Vulture, have him show up at the beginning for some James Bond teaser action scene and we never see him for the rest of the film. That doesn't take too much time away from more important story elements, but still provides a fun action scene at the beginning and works if Shocker doesn't have any characterization to speak of.
I also think Shocker and Vulture fighting Spidey at the same time, makes for a better physical threat then Spidey taking on these second stringers one at a time.