I think the National Football Leagues playoff procedures are designed around providing fans the maximum amount of excitement while at the same time making sure the two best teams in the country are able to meet for a finale, I think that tweaks and modifications should always be made but the core system is a solid one.
I am an American and do not watch much soccer here in America, let alone other countries. This means, I am not sure how the playoff procedures work in England. I do Imagine that most everything has room for improvement. They do not want to get carried away though, because sometimes that ruins a good thing.
No matter how good something is, there will always be people who disagree with it. This does not mean that it is bad or that it needs to be changed. The NFL playoff procedures have served us fine for many years and I don't think there is any need to make changes.
I think that the Football Association's playoff procedure isn't a logical format. I think that they will not change it though since they've been using if for a long time in the sport. They definitely should change to a more traditional format where teams are able to eliminate each other after one game.
The typical bracket design would put all teams to play until eliminated. By the end of the tournament, the top two teams should have played the same amount of games. The way that the FA bracket works does not require that. The difference in games played could be up to five. This is a huge advantage for the team that has played less games. This allows for fewer injuries primarily due to stress and opportunity. All things should be as equal as possible in that final match. This one discrepancy is huge.