> If you use different fonts on each platform, the design will be slightly different

Oh no, the fonts will look different on different devices! Better commission a custom font.

Back in the day, we just accepted that was how the web worked.

Jokes aside, I see why you'd want consistency across devices and print. But what's wrong with using an open source typeface, or modifying one for your purposes?

> and other brands can easily buy the same things.

Why do you think a unique font is essential for branding? Some well known fonts are in use by many companies.