Hi there!
Here's the first update on the music improvement process.
I dug up the original track project.

All instruments were coming from a single huge FluidSynth soundfont — great for quick sketches, but nowhere near the quality of dedicated plugins or live recordings.
In the old project drums were splitted to many tracks so I could manually adjust volume/pan. With my Hydrogen-based custom drum kit I don't need that anymore, so I'll merge all percussion into a single track for convenience.
I also trimmed a few bars from the intro to make it tighter, doubled the crazy bass line with a piano two octaves higher, and moved part of the solo to piano as well (that run would be borderline impossible to play cleanly on guitar — especially with my current skill level :)).
Finally, I tweaked note velocities, changed the key to fit real guitars, and slowed the tempo by about 5%.
Here’s what the updated arrangement looks like now:

The next step was exporting the MIDI stems and importing them into a fresh Ardour session.

It definitely looks less pretty than LMMS — and editing MIDI here can be a challenge — but the sound quality and audio workflow are worth it. After these changes, I'm confident the new version will feel much stronger than the original.
Next update: upgrading the instruments (drums, bass guitar, piano) and hearing how the new arrangement comes together.