Your point #2 is misleading. Though he didn’t explicitly mention it, the battery he refers to is the high-voltage Li-Ion battery (about 400 V) not the lead-acid starter battery, which is 15 volts when fully charged (on most boats). (I can imagine that’s because he doesn’t understand the technology; he’s been seen ranting about mercury in energy-saving lamps in 2020, well after LEDs superseded fluorescent lamps in all applications.)

Still, the short-circuit current is unlikely to paralyze anyone swimming reasonably far. The easiest way to see if electric boats are indeed hazardous is death statistics. I’m pretty sure there are way fewer electrocution cases at sea than, say, gun deaths.