That is a bit simplistic, there are ways 'around' a hard cap too. But what is nice about it is that through restructured salaries, bonuses, etc, a team can 'go for it' for a year, two, maybe three, and pay the piper down the road. I like the idea of that system as it creates the most financially equal playing field among the sports and yet allows some leeway to overspend if you think that you are close to a championship . . . but you pay for it eventually.
No system is entirely equal btw, there are always ways outside fo the cap to spend extra funds. Scouting, facilities, players can get more advertising income in LA or NY . . . etc, etc . . . . but it is by far the most equitable among the sports in the NFL.