You don't need a x3 there since most cameras use a single monochrome sensor with a colour filter array on top – the debayering process can happen offline.
RAW format doesn't just mean an uncompressed image like a PNG. It's a direct readout from the sensor with minimal processing. It can be substantially larger than you'd expect just based on the resolution * bits per pixel.
You are correct, but don't forget the Bayer encoding that makes things smaller!
Good point! But in the other direction, don't forget that even those there's less "pixels" than expected from the sensor, there will be more than 10 bits per channel, typically 12 or 14. I shouldn't have said it's larger, not necessarily - but it's definitely not 1:1!