Chiefs were in a better position to draft Mahomes than we were (if we even wanted him). They have Alex Smith to start this year and let Mahomes sit and learn. The Chiefs also have a great coaching staff topping it with Andy Reid to coach him up for a year.
The Bills on the other hand, we don't have that proven starter (meaning if Tyrod fails, everyone would be calling for Mahomes and he would be thrown in way too early and fail). On top of that, I'm not sure we have the competent coaching staff to coach up a raw QB like Mahomes (or any of the QBs taken in the first).
Chiefs got a good deal for the future and I think we got a good deal too.