Disagree, or at least if there's a width that's too wide then I haven't found it yet. Let the user set the width they want in their browser, don't force your own max width on them.
Typography people generally agree that lines that are too long are harder to read and recommend fairly short lines, less than 15 words. They have a number of studies backing them up. Maybe you're an outlier.
For a long time I used to just disable CSS in Firefox (View, Page Style, No Style), which gives a readable page most of the time. I knew about Reader View, but because it only allowed low contrast gray text, and because I already had a workable solution, I dismissed it at worthless.
I recently noticed that I was using No Style so frequently that it would be worth checking for a better solution. I found it's possible to fix the low contrast text in Reader View with custom userContent.css: