Saints to interview Giants OC Mike Kafka [Interview scheduled for Thursday January 9th]

I mean he did spend 16 games and camp getting coached up and Mahomes says part of that was Kafka.

And if he was so clearly ready before he was coached at KC and it was obvious by watching the dude, why did he last until the 10th pick and why didn't Andy Reid start him in the first game of his rookie season?

I don't know what if anything Kafka had to do with Mahomes development, but it seems pretty clear that someone helped him get ready to start in week 17 and that Andy Reid at least didn't think he was really ready before then.
Alex Smith had his best statistical season in 2017. I’m sure Reid took a conservative approach, to try and get his elusive ring. It would have been pretty ballsy to throw a rookie in there, but I’m sure despite the blow back Reid would’ve initially received, Pat would’ve adjusted just fine.
Plus, some coaches make dumb decisions. Much like Del Harris not making Kobe Bryant a full time starter until almost year 3. It took injuries to 2 guys for Kobe to get a good consecutive starting gig. It’s not that he didn’t have the talent and gifts, his coach was just a stubborn.
Just bc guys are head coaches, doesn’t mean they are perfect or they make the correct call every single time.