There is unfortunately no way to measure this. By the same token though, you need to offer actual evidence that the merit limits notably deteriorate the average player's gaming experience. Which, such evidence would be just as hard to come by for you. Testimonials of a handful of people on a forum (for either side, mine or yours) do not have statistical significance.By the way, a supported argument would offer evidence to support it. In this case, it would need to offer evidence that keeping a limited merit system notably improves the average player's gaming experience.
A more reasonable thing to measure is if there is a meaningful amount of variation in merit point combinations in use. The problem here is the only data we are given by SE lumps everything together. You can only see the total amount of people with one or more levels of each merit. You can't see all the individual combinations in use. Attribute category for example isnt a great measurement because there are more melee-based (STR) jobs than ranged jobs (DEX, INT) or support/specialist jobs (MND/AGI/CHR). So if everyone set their attribtue merits for the one and only job they play most, I would expect to see more STR merits than other merits. But this doesn't mean everybody plays STR based jobs nor does it mean nobody uses other combinations. (e.g. if your true love is mages and you don't use melee DDs or tanks much, you're not going to merit STR)