I think we‘re in a very different situation right now. Proton has become so good that it‘s just not necessary for most developers to do anything to get their game running on Linux. When Macs peaked in the hardware survey, the compatibility tools were far less powerful and developers had to actually invest time and resources, if they wanted their game running on Mac.
I also think that the Steam Deck is absolutely being recognized by many developers. Even big publishers proudly announce their games being playable on it. And having games optimized for Deck often improves them on Linux in general.
So I really wouldn’t worry about developers not specifically targeting Linux. Even without that, gaming on Linux is in the best spot it has ever been and is steadily improving.
There‘s a great video on that topic by Matt Parker (Standupmaths) which I‘d wholeheartedly recommend.
TLDW: No, terrain elevation isn‘t generally taken into account when calculating a country‘s surface area, though the actual method differs slightly from country to country. Switzerland would be around 7% bigger, if its mountains were to be taken into account.