1&2) Zay was the 37th pick in the draft. Buffalo traded pick No. 44 and No. 91 to the Rams in exchange for No. 37 and No. 149. In essence, we traded 2 picks to get 2 picks with about the same playabilty and ability to make the team and impact. Moreover, the BEST time to move up is when the coach has previous experience with someone. It offers less variables. I guess Rex had experience with Sammy as well when his son was the long snapper at Clemson (sarcasm btw).
Sammy Watkins was the 4th overall pick. The Bills sent the ninth overall pick (one pick) along with their first (second pick) and fourth-round (third pick) selections in 2015 to Cleveland in the trade. So we picked up 1 impact position instead of 3 - on a team without the certainty of a franchise QB and questionable talent. This entire argument is silly and a non starter if one finds equivilance between the two.
3) That is ANY position in a draft. However, your premise is correct - missing out on a highly drafted QB is not good.