It’s based on:
- Screen Size
- Display Resolution
- DPI (Which basically factors in the two above)
Generally, Windows wants your display to look similar to what a 1080p display looks like at 100% scaling on a 24" display, or thereabout. I don’t disagree with this. Anything less, and even my good eyes are questioning the decision.
This is also why even some 1080p Laptops come scaled to 125% or 150% by default (14" or 15.6"). At those screen sizes, things may not be ergonomic for many users at 100% scale.
This means that it will suggest higher scaling if you have high resolution at smaller screen sizes, because even though the screen is HiDPI, it simply isn’t ergonomic to run it at minimal scaling. No scaling on a 27" QHD display is borderline unusable for me, personally. I’d have to scale it up to about 125 or so. UHD on a 27-28" display isn’t usable for anyone. It has to be scaled up significantly. I think when I checked, 175% was the lowest I could go before the display became unusable, and my vision is quite good.
This is also why no Apple Retina Laptops run at native resolution. They ALL run scaled up - even the “More Space” preset is scaled. Apple doesn’t even give you the choice. If you ran them at native resolution, you wouldn’t be able to see anything, and it would be the same as running a 27-28" UHD display at native scaling. Hook up a 24.5" FHD panel to a MBP and it won’t allow you to scale the display in either direction, because the Display Size-to-Raster ratio is already in balance.
The benefit of those HiDPI displays is not only the resolution, but also in the DPI (less pixelation, etc.), so the user has to find a “balance” that works for them - but there are extremes that simply make no sense regardless (to the point that it [literally] doesn’t make sense to allow you the choice to use them).
If Windows is suggesting 300% scaling, then I’d assume the display in question was in the 27-28" range… that seems fine. I’d probably go down to 200-225% as well, but … younger eyes, and all. In ten years, maybe not.
Many people opt for larger displays. I prefer smaller displays because I really don’t have like having to pan physically to see my entire display (gaming habits/preferences).