Not many applications are intended to be used on both.
In particular I think most applications for professionals assume you are on a normal computer, not a phone. Consumers, OK.
There's an entire class of professionals out there these days who don't use laptops. It's possible to run quite a sophisticated business entirely from a phone these days, and a lot of people who are doing exactly that.
Sure, there are professions for which this doesn't work - but even as a software engineer I find myself increasingly frustrated when I can't do things like review a simple pull request on my phone if I'm away from my desk rather than pulling out my laptop.
In 2012 sure, but with so much professional work being done asynchronously and mobile phones/browsers being so capable now mobile availability is table stakes.
A few features may be disabled, but if I log in and see a messed up layout or a "please log in from your desktop" screen it's a big red flag for quality/execution shortcomings that will bite me on desktop soon enough.
So I only have to build for laptop sizes and up. For what I do, anyway.
I should be able to go to HN and "View as safari on ios 15. | View as Chrome/brave/ as Device Type [X]" and assign it to ctrl+middle+shift+click... or some such...
I should, be able to see the view, on my machine between the three: Desktop, iOS, Android for the same URL view and see the interactions on desktop....
Is there a reason why one cant just cycle through these views on a single tab of a single browser?
Click the button and it just cycles through the view
Rendering with a specific OS/browser combo is not something you can do accurately without actually running that combo. There are services like Browserstack that will do this for you, but I don’t think it’s something that could realistically be built into a browser.
Tricks that work on desktop - where a web application might stay open in a browser tab for weeks at a time - don't apply on mobile. On mobile, I'm much more likely to drop into your app for a few minutes to achieve a single goal, then navigate away and un-load it again.
So assuming that I'm going to pay that loading price once and then keep interacting with your application doesn't actually work - most of my interactions with your app will be a cold start, often with an empty cache too since browser caches on mobile devices (especially cheaper Android phones) are much smaller.