If the fets are acting like a resistor, they will blow in a heartbeat or less. That can happen if the gate isn't powered properly.

No, the basic idea is to switch the fets on and off , with the off cycle longer or shorter to follow the commands. In short, you give the motor bursts of full voltage, and the nature of the thing will make that into an avarage.
Only specialised tools, like osciloscopes can show the pulses. the avarage multimeter will show the avarage voltage. And that's only worth something with brushed setups.

For a heavy, I prefer Iskra's atm. Easy to aquire, not to expensive and rugged to boot. Those are heavier than the magmotors, but thesadays , weight can be found in batteries. 10 or 12S 8400mAh LiFePo4 weights as much as 12V 12Ah SLA.