Browsers remember your zoom settings on a per-site basis. Try using it before claiming it will fuck up the entire experience.
> The user controls their default font size on their platform. What if they'd already increased it, and now I'm just making it bigger?
The person making the site however wanted someone to change their default font size
We have to also consider that the person in question is most likely not having a bad experience on every app and website, and that this guy just had a tiny font size on his site
Even this famously tiny fonted site is readable on mobile
Looks like in Chrome on mobile you can set it per site, but you need to dig into accessibility for that. I don't see a way to do that in FF, so you would have to set the default which would effect all sites.