For
Legendary we know already >
Amph = 28889 posts but guess what, he got only 1 merit

Interesting that for 28889 posts he only earned 1 merit. I was going through his posts and he is definitely no shit-poster. His posts are generally reasonably good but just really short so don't attract merit.
Some people spend most of their time just in the miners' sections. And end up posting more on some of the mega topics related to pools and equipment. And these users end up being unfamiliar with the rest of the forum. They are more interested in altcoins that are mining. Not so much in Bitcoins.
Not writing shitposts is not enough to earn merit. It is necessary to go to the sections where there is abundance in the distribution of the merits, like the Meta section.
I agree with what you are saying. It doesn't apply to that member but it does to many others.
While merit has been great at targeting shit-posters there are a smaller amount of people that are not shit-posters that just don't post to a level where they easily earn merit. I try to look for them because those are not people that the forum wants to lose.
I have had a look at some of the other boards and some of them cause me psychological stress. I just see no point at reading a thread where people express the same opinion over and over again and don't read any of the previous posts. If I hadn't discovered Meta and some of the intelligent life that post here I probably wouldn't be on bitcointalk much.
Mining is great for people that have specific issues but about as interesting as reading a telephone book for those that don't use those miners, algorithms or are experience specific issues. But a brilliant place to look when you have an actual issue and some super-smart people post there.