They aren't sidestepping the garbage collector nor the C# safety checks for the whole engine, because HPC# is only used in a very focused area, everything else is plain old C# as always.
I can also state that in the old days C wasn't worthwhile to be useful as a programming language to write game engines, because proper game engines were written mostly in Assembly with C, Pascal or Basic as their scripting layer if at all.
"PC Intern: System Programming : The Encyclopedia of DOS Programming Know How"
https://www.amazon.com/PC-Intern-Programming-Encyclopedia-De...
With examples in Assembly (MASM and TASM), QuickBasic, Turbo and Quick C, Turbo and Quick Pascal.
Then one can follow up with some MS-DOS classics.
https://www.amazon.com/Peter-Nortons-Assembly-Language-Book/...
https://www.amazon.com/Advanced-S-DOS-Programming-Microsoft-...
https://www.amazon.com/Peter-Norton-Programmers-Bible-progra...
https://www.amazon.de/PC-Intern-Programming-Encyclopedia-Dev...
I can also state that in the old days C wasn't worthwhile to be useful as a programming language to write game engines, because proper game engines were written mostly in Assembly with C, Pascal or Basic as their scripting layer if at all.
For example,
https://www.amazon.com/PC-Intern-Programming-Encyclopedia-De...
I pick "PC INTERN: system programming", 1992.
https://www.amazon.de/PC-Intern-Programming-Encyclopedia-Dev...