I never really understood why people want to style stuff like this. I like how you can express yourself by using colors and layout and stuff like that. But at some point usability is more important than branding.
Said no designer ever.
At work our design team came up with buttons that are 10x10 pixels on my screen. They are used to change pages (like on mobile, but this is a desktop program), the scroll events are ignored by design, so you either click the tiny buttons (which are slightly darker gray than the dark background) or you simulate a finger swipe via drag and drop with the mouse. Yes they designed a touch GUI for a desktop application.
Any designer unwilling to say this, especially in the context of accessibility, should be outright fired. They are bad at their job.
Accessibility is a legally mandated requirement, not an afterthought
The place where I live is very good at pretending to do the right thing while doing absolutely nothing.
For example a touristic social account managed by some government entity posted some extra complicated wheelchair lift (that will inevitably break in 1 month at most) to show how disabled people are well integrated.
Meanwhile of course the real situation is that people on wheelchair can go almost nowhere at all. Newer public transport has even worse accessibility than before, elevators are mostly broken at all times and regular ramps are missing, doors regularly have super strong springs and a button to open them (which breaks all the time) when they should just have a much weaker spring instead.
Designers I've worked with are like the tourist social media account. Showing the one single place they made accessible and explicitly saying in meetings "we are good people, we care for disabled people"… and then hating me for pointing out the million other things that are not accessible.
Of course they love to show off how good they are to the poor disabled people, but that doesn't mean anything until some government reminds us that we are in breach of contract unless we make our GUI accessible.
The second group does make things that look nicer, but the first ensures it can be used. You really want both, but then you need to be careful about who wins when they disagree.
On flipside, note that many regulations - in any human domain - are oriented to raise the level of the worst performing, not to support the efforts of the best or to optimise the middle.
Also I'm disabled myself, although not in a way that requires any adaptation to use a computer. But I of course notice these things a bit more than average; and I get to hear my elderly father's complaints about software that he can't use because of inaccessible design.
Of course a designer should be qualified and notice these things even more… but all they do is move buttons around and disable copy paste so that even fully abled people have a hard time using our software between versions.
Which everyone is only doing because it's an industry fad likely stemming from copycatting one or two instances where it was done for legitimate reasons.
And this also assumes that the browser validations are in any way usable to begin with. I would argue that they are not, and would require some sane styling to become usable in the first place.
And I think you're wrong.
Consistency with industry standards is a lot more consistency than consistency just within one silly "app" webpage.
I have never worked for any company or organisation that believed this. Most clients will send you their branding guidelines before sending their feature requests. If they get to choose between adding a new feature, improving usability or making sure everything follows the branding, they will choose the branding every time.
The issue here is, at what point does usability take precedence. Does input validation fall under "branding" or "function"? IMO, an error modal is nothing to do with company branding, etc. — it's not even part of your document, it's the browser's responsibility. The browser can decide to do something completely different from showing a modal as far as its concerned, so you shouldn't make any assumptions. Your responsibility ends at declaring what valid data is.
Having as little native anything means you go from n sets of documentation to 1.
This isn't an issue if everyone's an accessibly expert, otherwise we're sacrificing usability.
People like to complain about JavaScript on websites, but they often don't know in what a bleak world they would live.
I wish there were more lightweight websites, none spring to mind other than HackerNews, SourceHut, and Pinboard.
But for any more complex form with dynamic content, JS is still inevitable. I guess for HN the input form at the bottom is enough. But Algolia uses a custom input component already.
Zero JavaScript is rarely practical when there's meant to be interactivity of any kind. The issue isn't the language, but the appalling bloat that is now the norm on the web. And, course, bad design in its various forms.