In my experience, the original is preserved in these kinds of projects. QoL, tweaks, and others are optional. While some games may have taken slow downs into account, many did not. These projects, I would say, are the definitive way to play. Stay true to the original, or get fed up with outdated control methodologies and toggle on QoL changes. Devs are very attune to how these games were originally designed and don’t forsake the original. As for emulators, you can still very much miss out on the intended way to play - think crt scanlines. And emulators are quite literally a hodgepodge of tweaks to make the games run. One of the reasons projects like this were born - because people wanted 100% accuracy