Most Windows apps that are guilty of being slow and poorly made do not use the .NET you speak of at all. If they did they would work much better!
I’m hard pressed to think of any Microsoft software at all that I think feels really nice. Except for VSCode, which is of course built on Electron and not .NET.
The only thing that comes to mind is Paint.NET, which doesn’t seem like all that big of an application. It’s very nicely done, but I think it’s only got like a single dev working on it, so couldn’t be that big.
and in context to the thread files-community/files is great and open-source and .NET * https://files.community/ (its actually 96% .net and 3.1% c++)
Most of them. An implementation would have to go out of its way to make itself perform poorly if it is built on top of, say, .NET 8.
Have you heard of Ryujinx? Or Nethermind? Or Garnet? Or have you seen that .NET's Regex engine, written in pure C#, is the third fastest in the world after Intel's Hyperscan and Rust's Regex crate?
We are only just now wrapping up the conversion at work to .NET 8 from 4.8, so it will be interesting to see the performance numbers once that is complete.
Our .NET application has millions of lines of code, so JIT compilation time in particular in the old .NET could be very painful.
The difference between 4.8 and 8 can easily be tenfold, depending on the workload and bottlenecks (if it's a slow DB query - EF Core might compile it to a more efficient variant in, say, EFC 8, but if it's linear scan - not much can be done).
Edit: I stand corrected, based on reply in a sibling comment most of the perception stems from how .NET Framework works. Understandable.