Need clarification about STR scaling, classes, or if theres some bug on its scaling. Test video included

So found out after asking that STR really is not scalating exponentially, thats what i thought when i did read the website, more str = better str/patack ratio. But thats not how it works, after speaking on discord, it seems classes are related somehow, and we dont really know if this is intended or a bug, so help or clarification would be very much welcome. Test video https://www.youtube.com/watch?v=BQawT5QjU6U&feature=youtu.be