Also I basically know jack sh!t about really good wave boards, but to offer a mini-wave kook's opinion instead of just shitposting...
There are really good waves like Teahupoo or some waves at spots like that where there's a really square compact pit and you kind of have to get under it, and there's not the same early entry options as more open faced spots. IMHO going longer and relaxing rocker can set you up for some hellacious pearl/nosedive/whiplash into flats/absolutely industrial pressed by the lip/over the falls/spin cycle ass beatings.
I totally never tried to pretend I was a tube dude in Mainland Mex on my 6'10" one day after I got the slightest bit of confidence and kind of spun underneath and had exactly this happen to me or anything.
Then there are really good waves where the drop isn't an extremely late vert knife into the warped out pit. It's a little more open, rolls in and lets you kickstall and set up the keg...these waves IMHO you can absolutely get away with more length and a little less rocker to get more paddle/positioning/early entry.