I think most of your concern isn't actually relevant to this case. The point of the article is that default numeric input basically just fundamentally doesn't w

I think most of your concern isn't actually relevant to this case. The point of the article is that default numeric input basically just fundamentally doesn't work unrelated to wanting "branding", it just doesn't validate user input in a way that is acceptable to either users or product owners: even if you wanted literally zero visual customization you shouldn't use it, and if you were building a native app you also wouldn't accept that behavior. And while there's a whole area about browsers becoming an app platform, this also isn't strongly relevant here because it's a meaningful problem even when building a trivial form submit. The choices here aren't branded vs unbranded, it's "does the website form submit validate user input or does it not validate user input?" Everyone wants the form to validate, and you can't reasonably validate input if you use that component, so no one can use the component.