The "inventor" of the 4-2-3-1 Juanma Lillo (at least he is creditet for inventing the formation) has in interviews stated the necessity of the high line / high pressure for it to work. It was, at least the way he's been putting it, a formation he came to think of as a formation were the soe plan was to win the ball high in the pitch.
One of the main plusses of playing a high line is not only that it compresses the area the opposition can use, but it also makes it easier for a team to support their attacking players faster. If playing a 4-5-1 of any sort and defending deep, one would very often use to much time to get into atticking postions (and the need of a striker who can do something by himself and/or hold up the ball while waiting for support). Today, with players incredibly fit and able to run far more than 10-15 years ago, it has become far easier to defend against teams drooping deeper as you can normally get into a sound defensive shape quicker (or at least just as quick) as the attacking side. Thus, if you drop deep you'll either have to resort to the long ball out (who rarely is succesfull against good teams), or you'll struggle to create anything noteworthy as they'll be organized by the time you get to run at them.
By playing a high line you open yourself at the back (and especially if your players are like Dawsone, that is not suited to it at all), but you'll also have a far better chance of cathing your opposition out of balance. Thus, playing a hihg line might not be all good, but as I see it, playing a deep line will rarely work better, and certainly not over a full season.
