There seems to be 2 schools of thought regarding this.
One is what you're saying, and indeed I would rather give a merit to someone who is still trying to rank up than a Legendary. However, I do give out more merits to Legendaries than I should, simply because I tend to interact with them more, as the crowd I roll with.
The other is that Legendaries get more merits than they should simply because they are Legendaries... As I type that I realize it doesn't make much sense, but that's what some people truly believe.
I think it depends if the Merit sender is short on Merit or not. If you're not a Merit source, I can imagine you prefer to send the few sMerit to a user who "needs" it (as long as their posts are good). But if you're loaded in sMerit and have a hard time trying to use them all, you can just as well send them to Legendary users too.
However, since I've received Merit from
413 unique users, and I had a Legendary rank already when Merit was introduced, it's safe to say many users Merit higher ranks too.