Never underestimate teams. Your mentors are right that nothing you build before the build season can be used on the competition robot. And there is no way (at least in the spirit of gracious professionalism) to get around that rule. In fact, there are limitations to what you can do with CAD models that you make during the offseason. Of course, the rules about that could change next year, but the chances of that happening are slim and not something you should expect.
So yes, teams really do build swerve drives in the offseason just to do it all again during the build season. And not just swerve drives. Building practice robots in the offseason is a practice that countless good and great teams do. Why? Because the offseason is a time to try out new things, to train your students, and to get new students excited about the upcoming season. And in my opinion (and I'm definitely not alone in this opinion), a practice robot is the best way to accomplish these things.
I'm saying this because I know from experience. Last year, my team didn't get to build an offseason robot, and test out a new idea we had. But when the build season came, we decided we wanted to use this new idea even though it was untested. So about halfway through the build season, we realized that BECAUSE WE DIDN'T PRACTICE IT IN THE OFFSEASON, weren't going to be able to do it in time, and had to scrap the idea and with most of our progress. From there, everything just became a disaster for our team, trying to make up for the time we had lost. We ended up working ~75 hours during the last 7 days of build, and yet we still failed and ended up finishing our robot at our first competition; we didn't even get to compete very much. As a result, our robot never reached its full potential, and although my team still had an awesome season, it could have been MUCH better, if only we had built that practice robot.
Edit: I need to learn that every post doesn't need to be a full out essay
