Actually, I think the laserdisc source is already - sort of - subsampled. Isn't the composite analogue video signal in NTSC YIQ format? This format uses a similar technique to reduce the analog storage required.

I also think that many capture cards use YUY2 internally, which is YCrCb at 4:2:2, since this is the digital equivalent of YIQ. If you ask for RGB output, then what you get is just the YUY2 data upsampled. Since huffyuv is much better at compressing YUY2 than RGB, it is better to stick with YUY2.

The chain is:
Analogue YIQ
-> Digital YUY2 - uncompressed, 4:2:2
-> huffyuv - compressed (lossless), 4:2:2
-> MPEG - compressed (lossy), 4:2:0