You shouldn’t have any users at TL4 unless you manually put them there (it’s an admin-designated level). As the others said, you should just be able to set the default level for new users at TL2 and make the entry requirements so low that basically everyone gets there almost immediately. Then you can run a command to ensure that everyone gets immediately put at their automatically-assigned trust level (with the exception of locked users).
If you have users with locked trust levels (and want to get rid of that), this should help.
Edit: Just saw that @rorycb gave a much more direct way of doing this. That’s probably the better option.