The AFL actually ended up being a good deal for the NFL.
The AFL opened up the game, increased scoring and broadened the appeal of football.
Al Davis was the AFL commissioner who was negotiating with the NFL. Lamar Hunt and Bud Adams went behind Davis’s back to make a deal with the NFL.
Davis wanted all AFL teams accepted by the NFL and was willing to wait another year to make it happen.
Hunt and Adams wanted an immediate deal and bowed to the NFL demand that only certain teams would be accepted.
That was the beginning of the bad blood between Davis and Hunt and the Raiders and Chiefs.
All the AFL teams got in, plus the Colts, Browns, and Steelers moved over from the old NFL (which had 16 teams in 4 divisions) to the new AFC (which had 10 teams) to even things out. Nobody was left out.