I posted my previous post in feedback too.
And dialabrain is right, once you select a story you can type command+ two or three times to increase the font size of that specific story. Helpful but annoying if you have to do that for every story, which you do.
If you change the font size in Safari by clicking the "aA" icon (you may have to "Customize Toolbar..." to add the "aA" icon) and then go to another story in that same tab, the font size remains unchanged. This is very convenient.
I'd love to see that feature added to Mojave's News app. I will send feedback to Apple.