Always great to see more people trying out this veritable STG DeLorean! Was reminded while playing a few reacquainting credits, Icarus has some badass Omega Fighter Special scores.
RE timewarp shenanigans... I became aware of it when d0s posted about MAME being way easier than his PCB, circa 2018, due to zako not firing aggressively enough. That was right around the ACA version's release, which is board-accurate (as is MAME, after being subsequently updated).
Incidentally, another UPL-produced (though NMK-developed) late 80s STG remains inaccurate in MAME right now;
Task Force Harrier, which features a charmingly involved slowdown routine. Basically, your ship speed is constant even under heavy slowdown, with the code cranking up your horsepower to compensate, even as the world around you grinds. MAME lacks this feature, leaving the ship in perpetual overdrive. Actually kinda refreshing, zipping from end to end in a ruggedly Toaplanesque
Fast Aimed Shotter context, but undeniably over-easy.
I wonder if there was some crossover/comms between the two companies' personnel? Seems conspicuous, with Omega Fighter basically letting you do the same thing to enemies via its bomb. Might just be an odd coincidence, ofc. Harrier is also one of the precious few army STGs to dodge the dreaded Invisible Desert Stage Bullets, by palette-swapping them from yellow to purple as needed.