As someone who has done every side quest except some of the post moogle and crafter/gatherer quests, the side stories in this game are definitely not low-quality. Even the ones that appear in little settlements you pass through in the MSQ will tell you all about the life story of this one person who needs a fish or some meat, as if SE actually care about story-telling compared to other games.

So the Endwalker role quests were bad. Really, REALLY bad. Absolutely atrocious, in terms of pacing, presentation.
The one thing I will agree with is that I knew I had to kill something, but they acted like I, the Warrior of Light, couldn't kill it and needed to do some sort of preparation first. It felt absurd and like the quests were filler until max level. Some of the role quests were less filler and more engaging than others. Getting to know the characters in each was interesting but when you know it's filler it's harder to appreciate it.

While the ShB role quests utilized characters previously established in the MSQ and further fleshed them out and gave them proper conclusion, the EW ones revolved around literal whos who became blapshemies, who I could not possibly have cared about.
This is not correct. The EW role quests utilized characters previously established in the MSQ including the city state politicians and other established characters like Fordola and Arenvald, and gave them a proper conclusion.

They barely, or not at all in some cases, justifed the entire reason for needing your specific role, which is the entire bloody point.
They took advantage of the expertise of the city state politician, such as how Kan-E-Senna is a healer and have you fill in the gap. I found that the role quests tested some things about the roles, knowledge of tank interrupts or making you actually have to heal.

it makes zero sense for you to do the EW quests during MSQ, and I do not believe for a second that there are still blasphemies roaming about post EW.
I felt the same way, but one of the quests clarified that it would take time for the final days effect to wear off even though we stopped it.