In the storm of Doom-Quake mania of the mid 90s there was Chasm: The Rift by a small Ukrainian company Action Forms. And if memory serves me right, it was created in Turbo Pascal. It was late in development and came out in 1997 after Quake, so it didn't get much traction. But the engine, though pretty limited, could produce 3D enemies with interesting effects not found even in Quake.

So Turbo Pascal (with a whole bunch of x86 asm inclusions) was totally capable of producing Quake-level games. I myself, in the late 90s, discovered the hidden capacities when I learned x86 assembly from Peter Abel's book. Once I got rid of the primitive TP BGI library and switched to VGA 13h, it was an unbelievable level up in abilities to manipulate pixels on the screen!

I don't see why it couldn't have been written in Pascal. Plus, Quake was written in C/asm, not C++.