I wish there was a way to find out how the latter would behave in FPC+SDL, without actually porting it first.
Well... there is no way even
after porting it...
You can't compare Linux vs Windows performance... They're too different. One does better one task, and another task is solved better by its adversary.
In Castle Game Engine i get ~60 FPS with ~400-800 sprites (rendered in non-optimized way) at 5-10 years old computer and ~30 FPS at Android tablet and 15 years-old computer.
I think its not efficiency but convenience is the main problem. C(++) was used to make games for a very long time and many games are actually written in C. That means you can find lot's of ready libraries, patterns, examples, answers, tutorials and support. Many C tools have been proven by time and excessive use.
Many game engines use C++,C#,Java,Python, etc. as scripting language, but you can hardly find any quality and actively developed FPC game engines but GLScene and Castle Game Engine, afaik, none of those can provide you with drag-n-drop interface to create games like Unity (C# based), you'll have to do everything by code.
So... I like pascal. I write my games in pascal. But I understand, that usually people don't write games in pascal and there are good reasons for it
I do it for fun, so, I don't care about obtaining the highest quality and productivity - I want fun
But if I'd had to do a commercial-level game I might would have changed my approach.