Alright, so first and foremost 540p *IS* a Resolution.
You have 3 Linear Resolution Scales.,
540p (SD) > 1080p (2K) > 2160p (4K) > 4230p (8K)
480p (SD) > 960p (SD) > 1920p (3K) > 3840p (6K)
360p (SD) > 720p (SD) > 1440p (2K) > 2880p (5K)
Scale 1 is the PAL Standard
Scale 2 is the NTSC / ATSC Standard
Scale 3 is the LDTV Standard
Yes, I'm aware the SD Resolution is more typically listed as 576i/p but this actually only displays 540 Pixels Tall because of accounted Overscan.
This was dropped for High Definition as Digital Displays no longer were required to Overscan for Full Panel Display... This is also why either NTSC or PAL Scales are considered FHD / UHD., where-as LDTV are HD / QHD.
LDTV as a note is a Video Format not a Display Format., developed by Sony.
These differences on Analog displays was never a particularly big deal, as Natural Aliasing would resolve the Pixels without any Display Scaling Voodoo but Digital Displays this is an entirely different story.
If you've ever wondered why 720p looked fine a decade ago (with HD Displays) but now on FHD/UHD it looks absolutely terrible... the reason isn't because it's a Lower Resolution, but because the Outer Shell of Pixels has to be Weighted Blended instead of a Simple LERP. This produces a Soft (Gaussian) Blur to the entire Image instead of being Pixel Sharp... something that again on an Analog Display would be easily handled via Natural Aliasing and appear no different, but on a Digital Display is distractingly noticeable and makes the Image Quality far worse than the Resolution should be.
This is especially true with Real-Time Display Scaling approaches that have to be relatively inaccurate to maintain performance and reduce latency as much as possible, but because they have to take extra cycles to perform said Scaling; again this is what introduces the infamous Input Latency issues in Modern Games at said Resolutions (on Standard 1080p Displays) compared to Native.
Overwatch has Display Scaling built-in., you can see my point by simply changing it to 50% (which on 1080p would be 540p) and 66% (which would be 720p, but you'll have to set that Manually via the Configuration File as Blizzard disabled such Percentages to prevent the very issue I'm talking about above).
< • >
Now as for the Windows 10 Requirement (despite using DirectX 11)... well without getting into a rant about Epic, DirectX 12 Support in Unreal Engine 4 is beyond worthless. They don't actually support DirectX 12, but rather DirectX12on11 (which Microsoft rebranded 11.3) which provides some limited improvements such-as Multi-Threading, Few Draw Calls (Shared / Optimised State Updates), Asynchronous Compute, etc.
Performance is better, but as a note while DirectX 11.3 does work on a wide range of GPU it's still a Windows 10 *only* API because it relies upon the changes to DXGI that exist only on that Operating System. Yet more than this., each Windows add more improvements than simply a new DirectX.
Universal Windows Platform for example., streamlines Development across Multiple Platforms and provides better Security, Update Deployment, Removes Reliance on Legacy Libraries (which improves compatibility and stability), Securely integrates Xbox Live, etc. etc. etc.
Heck even something as simplistic as the Multi-Threaded UWP Libraries, vastly improves the Performance and Lifespan on Classic AMD Processors such-as the K10 and Bulldozer that lack Hyper-Threading but have Physical Threads. This means instead of their Weak Single Core IPC making it unpleasant to game with them today and holding back the Graphics Hardware... you're getting more respectable Mainstream Multi-Core Performance.
That's simply not possible even on Windows 8.1 using the old UWP approach that's Single-Threaded.
As AMD Consumers / Loyalists we should actually be heavily in favour of Microsoft' push with UWP, DirectX 12 and Windows 10; because it provides a Level Playing Field for Hardware that simply hasn't existed in the Intel-Centric previous iterations of Windows.
The same is true when people cry about this being "Only Available via Microsoft Store"... any not available on Steam.
So what? How else do people expect Microsoft to actually get people to use their Digital Distribution Platform without Exclusives?
People so often rag on Microsoft., but honestly their Windows Store experience is reasonably good. This isn't to say there isn't room for improvement, but autistic screeching people do about it being "The Worst" and "I Hate Microsoft" is about as useful as a Chocolate Fireguard.
Microsoft needs to push people to actually try and use Windows Store, just to get support from Developers / Publishers to also actually use it.
Using their 1st Party Titles to do this, isn't just Sensible but frankly Necessary. Getting everyone on Windows 10 (by making said Store "Exclusive" to it) again makes sense because instead of Half-a-Dozen Windows Platforms with their own unique issues... now Developers only have to worry about a Single Platform.
This actually makes it much more Developer / Publisher Friendly and reduces the overhead required to support Legacy OS / Products.
What's more the Purchase Once... Play Anywhere, is frankly better value than any damn Steam Sale.
As now you're no longer choosing between your Xbox / Mobile / Desktop Friends; instead you can play with any and all of them... yet this actually goes beyond just Games, as it's also the case for Work Applications such-as Sketchbook Pro, Photoshop, Premier Pro, etc.
Single Purchase... use anywhere with device optimised support.
There are complaints I have about Microsoft Store, to be sure... as they need to improve the Search, UX for Product Listings, bring back the Music (sorry but Spotify and Mixer are Garbage), add an additional Tab for purchasing Hardware (such-as Mixed Reality, Controllers, Consoles, Keyboards, etc.) which at present are only available via their Website Storefront. Also I think a better / more visible showcase that every purchase provides you with Store Credit., I think it's like 1 - 5% depending on your loyalty rating... but that adds up quite quickly. I mean I literally was able to purchase Forza Motorsport 7 for "Free" because of the Microsoft Credit I'd accrued over the year before. This is on-top of their Refunds Policy which is inline with most Retail Stores.
This isn't even getting into how insanely easy it is as a Developer to Use and Manage your Products, Updates, Support, etc. while Microsoft takes a smaller cut than Valve.
Consumer impressions about such things are stemming from just general Anti-Microsoft sentiment NOT from their actual bad experiences from the Product / Services available. This has always been the way of things too. While I get why it's popular to hate on a Dominant Brand like Microsoft., it's quite bizarre you don't see as much hatred levied at Valve, Google or Apple who are much more prone to very shady practises that even make 90s Microsoft look like a Tame Kitty Cat (which is when they were at their most predatory... Microsoft today isn't even close to that., they've become too soft and consumer-centric; which isn't a bad thing)