In case anyone is wondering why that doesn't help the OP's issue... In order for the potatoes to be soft on the inside, you have to gelatinize the starch. That means bringing the temperature up to about 60C. However, this results in a gelatin-like block -- no matter how crunchy the outside is. If you want the inside to be fluffy you need to subsequently crystalize the gelatinized starch. You do that by cooling it down. If you've ever eaten cold potatoes or rice, you know how dry it seems -- that's the starch crystals. If you then heat it up again, these crystals re-gelatinize, providing a fluffy interior.

It's often good to go through the cycle more than once, which is why you see recipes for "triple fried" french fries. I tend to like to blanch in salted water, freeze, blanch in oil, freeze and then fry. This also dissolves some of the starch on the outside and provides more surface area for the oil to create crunchy bits. Yeah, it takes all day...

Never been to In-N-Out, so can't comment on what they do.

Yes, then they are just stiffer and hotter. Well done is better but not great.

A fry should be crispy on the outside and fluffy on the inside which is not gonna happen with taking a fresh potato and frying it. Freezing and blanching before hand make for better fries.