Its a huge shame most people never got the chance to play it properly until the cv1000 emulation was a thing. I can understand why shmup fans never cared a lot about it.
Thank goodness I got a copy of Ibara as soon as i got my first ps2 (around 2007), and learned about cave and yagawa from it and was basically the reason why I went full shmup back then.
Playing it on a rotated crt was a hell of an experience, and is the reason why i never complained about how shitty that port looks if you play it on a hori setup. That's why its still on my shmups top 3 list.
IMO Ibara is far superior than Greg, It has better music (Hosoe>>>>>Namiki), scoring is more fun, the attack mechanics are better (aura damage my beloved), and has more variety overall (trains and thongs>>>>gritty artstyle).
Got into Garegga 15 years ago and my first impression was that the game played like a bad prototype of Ibara. learned to love it eventually, but I still think is not as good.