MMOs that make the base content too difficult die because they can't sustain a large enough player base to cover development costs and make players feel like there's a thriving community. ("OMG this game only has 100,000 active players it must be trash I quit!")

With MSQ essentially required to progress and unlock all side content (hard or easy), the MSQ itself must remain easy.

You can't keep incrementally raising skill cap as the story progresses because not every player has the same skill potential (especially if there are physical limitations). Players tend to quit when they reach a roadblock to their skill level that prevents them from progressing farther.

There also has to be the desire to improve when those obstacles are met. Someone without that desire isn't going to rise to a challenge.

In the end, this is a game for entertainment purposes and not a self-improvement course. Look for it to be designed for those who want entertainment, not those who want self-improvement. If you're looking for a constant flow of increasingly harder challenges to overcome, this may not be the game for you.