Huh? Those are the original MIDI versions of the music, which is how Bobby Prince composed them on a Roland SC-55. There is no more authentic sound.
I doubt anyone in 1993 thought the OPL2 version of the music sounded better. General MIDI was mind-blowing in comparison.
Presumably most midi game composers checked that their music didn't sound like trash on the AdLib sound card most users would actually have? Good music that's actually written for AdLib can be extremely good, check out Stephane Picq (who sadly also died recently).
The TFX intro is some genius level AdLib programming. All other versions sound pretty weak in comparison.
https://youtu.be/YhQl_waHXoQ
It sounded great on my Gravis Ultrasound with custom midi samples.
(it was also a pain when the Sound Blaster compatibility was needed, dma 1 irq 5).
In 1993 I thought the OPL2 version sounded better and still do now.
But my broader point was that comparing this old game music to "real" guitar music kinda takes away from what it actually was for a lot of people listening to it - something different to and unique from mainstream rock/metal. It always made me a bit sad when these guys did interviews and talked about listening to ordinary rock bands, it kinda broke the spell that games were a special little place for people who were into computer-based art for its own sake.
OP is right. A waveform generator chip is a much more "real" musical instrument than a glorified sampler.