I do agree that there is an issue with having easy only content, it does not help players improve.

Best thing SE can do is make solo content a bit harder (MSQ & job quests). Let players run into that wall where they have to retry the quest multiple times until they get it right. The key word here is solo, so the players can take their time to learn. No need to wait for queues or feel the pressure of failing multiple times in a party. In the end, everyone is going to clear MSQ & job quests thanks to echo buff.
No though you are entitled to your on opinion. The last thing a company should do is increase the barrier for entry or difficulty in the main story. The MSQ is where most content is unlocked. It's bad enough people have to wait on queues, sometimes a long time. Playing XI some content was considered too hard for standard players, some of the genkai quest(mostly solo job quest) had some players quitting the game due to frustration. Half of the player base did not even get to through the CoP expansion which was not even the difficult endgame content locked behind it, until it was nerfed to high heaven years later.

If they want their main target demographic to be bleeding edge difficulty they could do that but I doubt it. For side content they can make content give headaches, vitriol, finger gymnastics, twitch reflexes, content so hard it makes babies bleed. But keep that away from the MSQ.