That ESC was designed for a 1/10 scale application
None of which require a servo that have 333oz of torque
That servo pulls alot of power from the system. So you cant really blame Castle or another manufacture of your going beyond the designed spec of the esc. Even though the esc works great for 1/8 buggies that was not its intended use. So the trade off is you need to run an external BEC. Which is very small by the way