It's like really late so this might make no sense at all, but could you scale these in terms of amount of maps in each subset?Which subset - the song length categories, or the diff spread categories, or both?
It doesn't really help to know that there're more plays on easy diffs on shorter maps than longer maps, since that's probably going to be the case anyway because there're way more shorter maps overall. More interesting would be to see if the proportion of easy diff plays goes down or not as we reach 3-4min long songs.
And what do you mean scale by amount of maps in each subset? Do you mean something like average (or median) plays / map?
I think it's difficult to extrapolate if more maps of a certain length and difficulty existed, they would get more played or less played. I'm assuming that significantly fewer mappers will map 4 min full spreads, but the proportion who will stop is also up in the air.* I'm tempted to make an informal survey of users, something along these lines:
1. What's your rank?
1a. What difficulty of map do you play most often?
2-4. Do you think there are enough Easy/Normal/Hard 4 minute maps?
5-7. Would you mind fewer Easy/Normal/Hard 4 minute maps? (*the thing is, we don't know how much fewer)
I frequent /r/osugame and surveys there get a lot of responses. I assume they're mostly representative.