It seems like increasing rank in the early stages is very difficult due to the high requirements compared to the next rank.
It only looks that way cause you're starting from zero at the beginning, so the percentage increase is higher. There used to be no merit requirement for Jr member, it was added in due to high spam rate. The original idea was to earn enough to get to member rank and rank higher from there.
When you look at the numbers increase, you need 9 more merits to move from Jr. Member to Member,
90 more to move from Member to Full Member,
150 more to move from Full Member to Sr. Member and it keeps increasing that way.
Anyone who has ranked up will tell you that the numbers matter more than the percentage.
More importantly, you do not have to rank up to use the forum. If you're just interested in learning and contributing your merit count doesn't matter at all.