I think you might underestimate the number/influence of casual curators.
I also think you might overestimate the upvote rate of regular and involved curators. 40 votes/day, every day, is a pretty large amount of upvotes and a considerable amount of time that most people can't spend on the site. Very easily achievable with bots though.
Still, someone who spends more time on the site will be exposed to more quality posts and have a larger sample size to choose from. He will still have an advantage over the casual upvoter. i.e. If I told you you need to find newly created high quality content in the next 30 mins, you'll have a much harder time than if I gave you 5 hours.
40 votes isn't so much. As part of a deep curation team, I'm probably least likely to misestimate the situation. Daily, there are approximately 3000-4000 shit posts, 200-500 posts worth a read. 50-100 are very good - well worthy of upvotes. About 10 are excellent. 5 is nowhere near enough - at that point all curation on the site will grind to a halt.
If you read the comments, pretty much every regular curator is opposing this proposal for this very reason. For me, it's clear there are 50-100 posts every day that deserve my upvotes. With a 40 votes/day target, it's possible to vote on all with voting weight control. With 5, curation - in the true sense of the word - will halt on Steemit.