Also, do such games generally perform better through native Mac App Store versions compared to browser-based or emulated ones?
I would think so. Browsers and emulators are not "light-duty" apps, so you add the browser's or emulator's overhead to that of the game and OS.
It could be internal heat. Macs have thermal sensors inside and can clock back the processor if the temps get too high due to workload. And remember, M-series Macbook Airs have no cooling fans, relying on convection cooling instead. Some here have issues with Macbook Air excessive heating but others like you have reported it.
If you have added any anti-virus or so-called "cleaning" apps, check your foot for a wound. Both can greatly increase the workload without retuning any benefit. The macOS protects itself quite well.
Those generalities are about all we offer here without more data. If you want a data-driven evaluation in this setting where we can neither see nor touch your computer, please post an EtreCheck report. We can quickly and within the limitations of these forums help you determine what issues are at play without our playing a protracted game of "20 Questions" with you that could go on for days.
EtreCheck Pro is available here:
https://etrecheck.com/index
The free version will do nicely for this purpose, although the app is worthy of our financial support.
We can see hard data about drive performance, software issues and interferences, and RAM usage. Etrecheck is the development of a long-serving and trusted ASC contributor. It is a reporting app, not a "fix-it” app, expressly for displaying information in these forums to help us help you remotely. It will not reveal any personal or secure information.
Please see this excellent user tip on how to post long text reports like EtreCheck's into a forum response:
How to use the Add Text Feature When Post… - Apple Community
Please post the entire report. What seems insignificant to a new Etrecheck user can hold answers for those of us who have reviewed thousands of those reports.