Everybody I have seen, including myself, who stuck with the trainer for longer than necessary and then moved to a sport plane talked about how surprised they were how easy the sport plane is to fly compared to the trainer. That's why I recommend moving to one ASAP. If you still need the self-righting characteristics to save you from bad piloting, then stick with the trainer a bit longer. But if you are in control for the whole flight, you'll just be holding yourself back from developing as a pilot by staying on the trainer.