Going with past experience, and with the 400 hour notion, I suspect the player caps out way before halfway point.
Rather than one 400 hour game, I'd much prefer 4 100 hour games, or even better, 8 50 hour games, in all of which the character systems work towards a specialized PC (and without the need to start neglecting things early on).
Of course the limitations that I specifically impose on myself are there. If I decide that the character is a bad shot and start deliberately shooting so that only every fift shot hits, of course the game reflects it; if I decide that the PC has https://globalhealthafricadotorg.files.wordpress.com/2014/04/leg.jpg and thus needs to move very slowly, of course the game reflects that, if I decide to neglect the level ups and character progression, of course nothing will happen to my character.
The point is that that should not be a requirement for the game by default. It shouldn't be the players burden to create a game inside a game in order to enjoy a game. Gimping and play pretend are all fine and dandy for iron man runs and the like, but out of the box, it should play properly without the player needing to concern himself with outside afflictions to the established rules.
There is nothing inherently wrong about a game that gives everything to the player in one go if the game at hand is geared for such kind of "go get everything -- and when in doubt, put on your gimp suit and gagball and have fun"; but what it does do regardless, is it removes half the intrigue from the character progression, encourages extensive grinding, and kills the replayvalue.
I can't think of anything more boring and halfhearted (keeping the context in mind) than a game with so loose mechanical setup that it doesn't even know it, that says "make your own". In that kind of situation, it would be better to discard all character progression save for item based (what point does it serve at that stage anymore to have these systemic hindrances if everything'll be open anyway).