I built a personal watercraft with four T200s. www.facebook.com/MantarayWatercraft. Early on, I used an IP68 rated thumbstick but eventually designed it out because it was uncomfortable and cost $158. It’s very hard to be steady with a joystick on the water. I used PWM with a port pair and a starboard pair using an Arduino. I started to reverse the opposite side motor after the turning side was +50% and the trailing side throttle was 0%. Using this method, I was able to spin in my own length
Later on, I switched to dual Hall-effect Scooter twist throttles and was much happier. I lost reverse (except for hard turns) but that was fine. I used I2C and loved the data that the BlueESC provided. Now that that interface has been EOL’d, I need to resurrect my old PWM code. I’ll miss having current usage reported so I can calculate remaining battery life (voltage is a bad way to tell).
BTW, I was using two 70AH Lithium batteries (LiFePO4 140AH at 13.2V) and would only get a couple of hours usage. I can’t imagine the Ryobi batteries lasting very long. I hope you have under voltage protection somewhere or you’ll kill your batteries.