Just some thoughts...
Doing the missions is actually pretty ineffective per hour. And doing the best meta powerplay stuff is not intuitive. My estimate is that "peak meta" should be in the 40-60k range and varies by power. For example, Archer can probably make 40k merits/hour bounty hunting, especially if you do it with friends, in the right circumstances, someone made a youtube video about it. Mining and 1ton trading can also give in that range or more, but needs a Power with financial alignment for best results. For AD, which I have more experience with, the top ten typically has several people making more than 1million merits, usually from plat mining in Yan Musu or Paesia. Iirc those places give us over 60k merits/hour with the right economy state, with less ideal circumstances in other systems it can go down to 8k/hour.
The thing is though, as everything with this game, knowledge and experience is rewarded. I am not a normal player by any means, but I can easily make 30-50k merits on useful objectives per hour, and probably more if I just wanted to max merits per hour. That means I could go from level 0 to 100 in about 15-25 hours, with the lower end being merits earned "selfishly" and higher time being merits earned on "strategy".
I suspect if you don't know what you're doing you'll be getting closer to 5-8k per hour, which puts maxing out the ladder at the 150hour range which is admittedly a lot. IMO this is a side effect of Fdev's poor explanations of how the feature works fragmenting the player base into "high information" and "low information" players, with Fdev having to balance against the high info players running circles around everyone else and the low info complaining because they are making no progress. Ideally the system needs to be better explained (and especially rebalanced for the parts "temporarily disabled" for the majority of the lifetime of the feature, THAT THE GAME STILL DIRECTS NEWBIES TO DO, WASTING COUNTLESS PLAYER HOURS!)