I think you are under selling Mayer as a receiver, he is far better then Ferguson in that regard, but as blockers, think Ferguson is comparable. Mayer might not blow you away with his athletic ability, but he knows how to find holes in the zone and catches everything.
I am in agreement with you, rather add a different type of TE that we already have on our roster with Kincaid. He is more of a modern day, mismatch type in the passing game. He is the best route runner and gets the most separation within the positional group. Not saying either will become these players, but it's like drafting Kelce (Kincaid) or Kittles (Mayer), just the matter what type you rather have as both are legitimate 1st rd TE prospects, especially with a weak WR class at the top.