Hey Seth,
You are correct that TL advancement is almost always dynamically affected by performance (read time, topics entered, days visited, replies etc) but there are a couple of caveats.
Firstly, TL4 is a level that cannot be achieved dynamically – a user must be manually promoted to that level by an admin because it affords people extra power as per Trust Level Permissions Reference.
Secondly, an admin can lock a user’s TL so that they don’t move up or down the levels. This is done on an individual basis.
You can also set the minimum trust level for a new user when you invite them.
I think the best way to achieve what you are trying to is to create custom groups outside of TLs but @JammyDodger is our resident expert.