150 additional merits to go from full member to senior member seems excessive and unfair frankly to those of us that were almost there. It will take years to reach that.
How cute...I am a potential Legendary member (only missing the post count) and I got only 500 Merit instead of 1000.
So be happy that you only got screwed by less then 150

Well B4RF, you have been a forum member almost as long as me, so you are correct that your post count has caused you to not move up in ranks, and if you had been at least minimally active in ever two week activity period, you would have earned enough activity points to have become legendary a year ago (something like that).
So, yeah, none of us knew this change was coming, but those of us who remained active benefited by this unexpected change based on activity level (which includes posting regularly).
I was actually active for many more periods then my activity is shown I think but I simply didnt do a ratio of 1 post per day.
And I dont really understand why a higher post ratio makes you more likely to be able to spread merit to others but yeah nobody knew this would come around so I guess everyone missing a rank by some posts needs to go along with it.
Btw I am not moaning since I dont really need the Legendary status right now since I didnt even used a signature campaign for quite some time.
I was just curious about the initial thought why this merit system has been implemented like this.
Nobody will do such a big change without spending much time about the consequences and benefits therefore I think there has to be a reason for this decision.
I think that there are a couple of points here that I could elaborate on, but I don't claim to know everything either, even if I have spent more hours on the forum.
Regarding activity, I think that if you are averaging more than 14 posts per two weeks, then you will get all of the 14 activity points for each activity period even if you only post a couple of posts in the most recent activity period. However, when you start to go below a 14 posts per two weeks average, then you receive fewer activity points. Something like that. So I have mostly kept my average up above 14 per two weeks, and I think that there was only a few two week periods that I did not post anything, so I did not receive any activity points for those few two week periods.
Of course, according to OP, the amount of smerit you received was related to your current rank and the amount of activity that you had in the past year. I believe that based on my being active for every period in the past year, I earned the maximum for my rank, which was 200 smerits.
Regarding rashness in implementing this system, it likely goes without saying that a guy like theymos doesn't achieve success in building/running such a large forum as this one without having some abilities for introspection and retrospection, so I doubt that this new merit system is built on rashness, arbitrariness or lack of weighing various possible pros and cons.