Well, you have a point of course and perhaps getting the necessary number of Merits for each rank isn't all too difficult (though I think it gets more difficult the higher rank you go).
I think the original intention of the Activity system is to reward active members who contribute to the forum, and assign a ranking for them. It is an own-merit system (my own unofficial term), meaning you yourself control the destiny of your rank. It has its flaws of course, as is the reason for now introducing an additional Merit system.
The only concern I was pointing out on the Merit system is that it is a subjective system dependent on others (and not an own-merit system). This means, you are dependent on not only getting recognized by others but also being favored by them to hand out merits to you. It's a system of chance, depending on whether someone notices your post.
All things said, this just represents my initial impression. Perhaps I could be amplifying the picture or perhaps I could have misunderstood the system, and my concerns may be unfounded. Time will tell how this unfolds.
There is an element of chance but it also depends on the quality of your posts. You get a better chance if your posts are higher quality. Compare to the old system where everyone had the same chance whether they post useless one-liners or broker Middle East peace.
The other aspect of the new system is that you're essentially competing with other posters for the limited amount of merits. In other words, you don't necessarily have to meet a specific criteria, maybe being your own self is enough. E.g. if 90% of the forum are shitposters and you're not - you should be fine.