I get what you're saying, and I was misguided in trying to project the idea that those players are wrong in how they approach the game. But I feel that there should be more incentive than just the system itself. Why should a ranking, be it on the screen or on a leaderboard, be the ultimate goal? Shouldn't the goal be just to play the game and get better because that's what you want to do, not what you have to do?
Not everyone has video capture software to show the world how amazing they are in combo videos. Often they resort to Special Bonus/S/SS/SSS ranking these games to test/validate their abilities once they've attained those skills and for the sake of a decent challenge from the developers once they've "Mastered" the game's mechanics (Which given that DMC1/DMC3 are notorious for their difficulty are likely to attract that sort of player). Hell, even the big-name players who pump out combo videos left and right do SSS runs because they find that challenge engaging and, really, there's not much else you can do.
Look at this game. You don't have mini-games or multiplayer to fall back on. You don't have Bloody Palace for a few more weeks (And whether that will hold a player's interest for any length of time will vary from player to player). All you have to look forward to is clearing the game on a certain difficulty, dicking around in the game, or going for SSS/Speed Runs of these missions.
When the hardest thing about SSS ranking the missions is having the 100% Collectible requirement met before the patch changes rolled around, you're sort of short-changing a very sizable audience of a challenge they would've been able to enjoy and have come to expect from these games all because of blatant design oversights that ANY DMC fan who spent three minutes with the series could say "Hey, yeah, this isn't going to work."