If everyone decides to not use this merit system because if he has no time or will to click the link, even if he likes so much one's post, everyone's rank will stop levelling?
Yes, however this is sort of like saying "If everyone stops using the trust system the nobody will gain trust ratings." While this is the case, it is a moot point, because it is not going to happen.
There are sources, and these people will continue to use the merit system even if they are the only ones doing so; this will of course monopolize merit in an unfortunate way, so it is in everyone's best interest to use the system as intended, rather than ignore it as if it were never mentioned.
This will makes ranks more valuable, disincentive spam and I highly doubt the 3-seconds it takes to merit someone will deter almost anyone. Are you that constrained for time?
Time is critical and when you're not a whale and have to partecipate and follow many stuff in order to gather coin dust, you tend to optimize the little time you have at disposal in order to not doing stuff that take you away time without giving some profit in return.
I don't see how and why someone who wouldn't even know me would give me some merit in order to make me rank up, so that maybe I'll take his spot in a signature bounty in the future and prevent him to join the very same signature bounty.
Also I foresee how users who know each others from long time will distribute merits among themselves even without proper well written posts. (I didn't read the rules accurately so maybe this is not possibile)
I hope this system will work out, but when you give power to users, it's a risk, there is always someone who will try to take advantage by cheat the system.