The question isn't particularly on-topic here.
Still, to address your points:
- S-Video is an analogue transmission method
- Firewire and USB are digital transmission methods
You can not compare these. You can't just say they "take more bandwidth".
S-Video is used to transfer an analogue video signal to a TV or some other device. It isn't that useful for transferring a video to a computer, as analogue transmission always leads to noise, crosstalk between channels, etc. and you would need to convert the video back to digital again.
Firewire and USB on the other hand enable you to capture the video from the camera as it is without a loss of quality.
S-Video or Firewire take a lot of bandwidth compared to USB cameras
That is wrong. Who said that? Where did you read it? If you want to compare, you should compare Firewire and USB, because they are digital (see above). But let's assume that you transfer the exact same video, then they both take up the same bandwidth.
What you might have meant was Firewire's theoretical bandwidth of 800 MBit/s and USB 2.0's 480 MBit/s
a tiny iPhone camera almost gives a better quality, speed, sharpness and looks excellent too
That is also absolutely wrong without taking into account the camera you are comparing the iPhone to. If it's a cheap Nokia phone camera from 2004, then yes. If it's a RED 4k camera, then absolutely no.
Does size not matter in this chapter?
Yes, because – simply put – with a bigger sensor size and bigger lenses, you will get more details out of the image (spatial resolution) as well as better light-efficiency. One could write a book about this though.