As others have stated, helps to have a solid OL and pro bowlers at WR and TE. Mahones is clearly good but he wouldn't be doing this in Buffalo with this supporting cast.
The jury is obviously still far out on Allen (and how he compares to Mahomes long term), but the point that we could have taken Mahomes and used a bunch of picks that we spent on Allen on other offensive talent is spot on. But that's the problem with having a lame duck GM, new coach, etc. The Bills were not in position in April 2017 to think through a good long term strategy for building the team.