Unfortunately, I think there's no way getting around the fact that a very good corner(especially when playing across from a very bad corner) just isn't going to have a lot of measurable stats. The result in most good IDP leagues I've played in is CB's are just devalued. Run stuffing LB's get valued to high and cover corners too low(relative to the value in the real NFL). Better to chalk it up as a quirk of fantasy football than try to "fix" a problem that really can't be fixed. Here are a couple things that help minimize the frustration imo.....
- DO NOT make CB tackles score very much. Otherwise, the best CB for any particular week is probably the waiver wire free agent rookie that was just thrust into the lineup because of an injury. I know some people think that fantasy football is best enjoyed when you grind on the waiver wire day after day but that's not as fun to me as team building.
- Make CB scoring more of a big play position. Still, bad corners will have more opportunities to make big plays if they are being picked on all game.
Really, this is my biggest gripe with fantasy football in general though. The mundane "counting stats" are valued way too high in fantasy football (tackles, receptions, yards, etc) and are almost always "opportunity based" while the actual big plays that turn the game in real football (TD, distance TD's, INT's, Forced Fumbles, Fumble Recoveries) are so much less important in fantasy football. To some extent I blame it on those making money in the industry because you can project counting stats much easier than you can project big plays.