I've read a couple stories that Darnold was the Jets' guy from very early on. They scouted him from the point he debuted. Maccagnan would fly out to Pasadena and watch him play, they fly home. He'd do it most weeks. He scouted the other guys, too, so it wasn't like he had blinders on. They were scouting all the quarterbacks from two seasons back, as they made a determination in 2016 that they could pass on drafting a top QB in 2017 and wait for 2018. But everyone in the organization that met Darnold, including the security guy at the dinner they had with Darnold, said, "This guy has it, he's perfect for the job." Yet all that time, the anecdotes depict the Jets loving the kid but being resigned to "watching someone else's quarterback" because they kept hearing he'd go #1, and if not, he'd go #2. Darnold, after the dinner, apparently told a Jets front office staffer that the Browns basically assured him he was their pick, and that based on the meeting he had with the Giants, he was pretty sure he'd be going there if not to Cleveland.
The other guy that the Jets really liked was apparently Mayfield. He was their pick if Darnold wasn't around. Third was Rosen. That was how they had them--Darnold, Mayfield, Rosen. They never thought they'd have the opportunity to draft Darnold and were speechless when he was on the board at #3. So, whether Darnold ends up being the guy, or the best QB in his class, the Jets evidently got the guy that they really wanted, and they did their homework on the QBs. Time will tell, but I'm very happy to have him.