Don’t mix up battery current and motor current. E.g. if you want to fry your motor put it in the vessel and accelerate. If you got a cheap ESC it will just increase the duty cycle till it runs 150A through your MOTOR. This one will work as a heater and all you see at your ampmeter at the BATTERY is the battery current. Which is how much heat you are producing.
See it from thermodynamics. You can’t destroy energy. So motor current of 150A but 0 RPM means 150A^2* R (in your case 0,03Ohm) in heat and 0W in mechanical power. If you look at your battery ampmeter you should see like 70W or ~2A (which are the 150A in your heater). And in a really short time your motor will burn.
Like that? Thats for a BLDC. I guess it is the same as for a brushed motor.
What do you mean by load? Power or torque?
By drawing more amps your motor will get more torque but not necessary more power (~0 rpm * high torque is still 0 mechanical power, and that is what you see at your amp meter at battery + a little bit of losses, but 100W in heat is quite a lot at stillstand).
The motor will draw whatever current necessary to achieve that rpm, but from the ESC first. The ESC contains energy and after the motor needs more it pulls more from the battery. The BLDC ESC is not just a switch between battery and motor.
So why can’t you kill your motor nor esc nor draw more than 2000W:
first I would check the motor amps. Test if your ESC really gives you 150A at full throttle. If yes, you did a damn good job with cooling the motor. Now you can buy a bigger one
Did you check if your ESC or the motor gets hot (and shut off), sounds like you get some throttling.
Or if your motor doesnt even spin up one time it can come from the sensorless design. Practically you cant power a sensorless motor. So what they do, they power up some phase and look what the motor is doing (using the other 2 phases) and then react accordingly. But if you are not getting a single rotation it might be an issue with the sensorless startup. Maybe try to start it outside the water and keep it running slowly till submerged.