Progear is great! But CAVE bullet hell patterns are already hard to deal with on a vertical screen, even worse when it's flipped, and there's also weirdo bullet cancel mechanics to deal with. It was actually one of the first CAVE games I've played, when I got the Capcom arcade collection on the Switch. One day I might be able to finish it, furthest I've got is start of stage 4?
Akai Katana has the issue of being locked down on MAME by Exa-Arcadia, cursed be their greedy name. It's not even their version of the game. Anyway. Good game too, I have solved that issue with a custom MAME build.
My thing with hori shmups, is that a lot of them are designed completely differently from verticals. They rely A LOT more on memorization, things come at you from way more angles at once, your hitbox tends to be HUGE and your shots pretty piddly at the start of the game. A lot of deaths end up feeling more like developer gotchas and unnannounced traps than an actual mistake on the player's end (that's why I hate R-Type), then there is the "Gradius Syndrome" that a lot of them suffer from, where if you die in an inopportune spot, you just lost your entire run, as it's very difficult or sometimes actually impossible to recover without all your powerups. And lastly, my eyes just aren't as trained to identify and follow bullets in a sideways orientation, I get hit by stuff I'd very easily dodge in a tate game. So, I'm playing more games like this to get used to these things, and learn how to employ them in my advantage instead! Call it a training arc, if you will.