Maybe we are talking about different things then. When you say Boyd is an ascending player I think of a player who is improving year over year and not just in terms of gross stats. I also think of a player who is climbing the depth chart and becoming their teams number one WR as well as the money and accolades that come along with that.
For me a WR #1 for a NFL team is a player who is good enough to demand double coverage and performs well anyways. Can win those double teams some times. Boyd got that opportunity and his numbers slipped Boyds aDot was 8 yards which was tied for 162 in the league last year according to
this. When you compare Boyds numbers to other WR with similarly low aDot and 100 or more targets like Robert Woods, Michael Thomas, Cooper Kupp, Jamison Crowder, Cole Beasley he is no where close to Woods Kupp and Thomas in terms of efficiency and more similar to Crowder and Beasley. This is kind of what strong was talking about too.
Maybe the difference is independent of Boyd and improved QB play is all it takes for Boyds numbers to be more efficient. Boyd was much better in 2018 from a efficiency stand point and had close to the same yards on 14 fewer receptions, so what you are saying has already happened before with Dalton playing 2 fewer games that season.
When you say ascending player I also think of one who is going to get increased opportunity and that seems unlikely to be the case for Boyd.
The Bengals did sign him to a 4 year extension so he is part of their long term plans. He got a similar contract to Crowder. They didn't pay him like a star WR.