> what a nightmare, now your website will look different to different people

That's what the web has always been. People don't all have the same display types, the same subpixel layouts, the same display sizes, the same DPIs, the same fonts, the same zoom levels... People use reader modes, global restyling extensions, per-site custom style sheets, full screen magnifiers, bounded/partial magnifiers, screen readers, OS high-contrast modes... the web has never been a fixed canvas that you get to paint on and then hand to users.