on what fps does your game run? not quite sure whether it's just placebo effect and me, but i capped fps at 60 through nvidia and things appear more manageable for me.

although i do recall some shmups executing commands on each frame, so having 30 fps would make everything extremely slow, while 120 would make things faster

I think mine is capped at 60 through NVidia as well and I can't even make it through the second stage without burning a continue with keyboard, gamepad, or joystick. I like the design of the game in general but it's way too hard to see what is going on - especially enemy missiles! I like bullet hell games but this one is punishingly difficult, and the fact that the powerups right right to the bottom of the screen and disappear sucks because if you want to have any chance of NOT dying, you need to collect those powerups every chance you can get. In most SHMUPS they float around the screen, giving you time to clear out enemies and avoid projectiles before grabbing them. There's a lot of times in this game where it's practically impossible to grab the powerup before it disappears.

try playing it in windowed mode and see if the speed fixes

Yeah, this is the most difficult of the three games, although tbh most of that difficulty is due to one level. Level... 3, I think. Ogoumo, or however it's spelt, is that one boss that always kicks my ♥♥♥♥ in.

Xaffiquel too, I guess, but the final boss gets a pass since, well... Final boss. It's supposed to be the one that pushes your ♥♥♥♥ in deep enough for you to start tasting it.

For Alltynex Second... I'd have to say Adoni. Actually no, lets go with the orbital death laser that Alltynex decides to try sniping you with

Reflex... In all honestly, nothing stands out in particular here. That games difficulty is more death by a thousand cuts (Or rather 7), moreso that any absurdly difficult boss. Maybe EBBS Entropi because of the interface ♥♥♥♥♥♥♥?

Ougumo is nasty he hard filters me.
I've 1cleared several Touhou games even a few on hard.

This game was PC only. No quarters needed.

I actually found Kamui to be on the easier end of the shmup spectrum... the difficulty is about the same as Layer Section/Ray Force, which is appropriate.

Ougumo is definitely a bit of a noob gate though, even the production Kamui fighters are less tricky*. The thing is, Ougumo only really has two 'gotcha' attacks - the stream of mines mixed in with missiles (don't use your lightning attack here, I know you want to) and the punch attack (Ougumo will try to corner you with lasers before the first one).

*they still kick my ass most runs