Unless I play from a forward tee, Valhalla is really not much fun for me to play, rough way too deep, too many long forced carries, stupid long uphill par 4s (#6 is maybe the hardest par 4 I have ever played). TBH, not a big fan of Nicklaus designed courses anyway. However, it is a great venue for pro tournaments though, can accommodate huge crowds.
Personally, while Olde Stone is also hard as hell, just seems more "fun" to play, the greens are wicked, first 4 holes or so are killers, but if you can get to number 5 relatively unscathed, it is not impossible to score on. At least IMO.
I made probably the best par of my life at #6 at Valhalla. Hit a drive off the toe and had 240 in - hit probably the best 3 hybrid I've ever hit and it caught the top of the bunker and stayed there, total fried egg. Blasted out to about 30 inches, total luck. I just took a super hard cut at it hoping to get it out. Still had to make a slick breaking putt to save it.
I'm a decently long hitter and tend to keep the ball in play, but you're right about the rough. I'm also not a great putter, and those glass greens will punish anything not struck really well and read properly.