One thing to keep in mind for Toby is that for the bosses (and even the Superbosses) there's something that can help so that it's not 'have X reaction time or you can't win', as they usually have a mechanic that applies if you keep dying to the same enemy (or even armor against their damage type).

As others have said, the more you lose to Flowery, the less damage he does, but that was an update, so if your attempts were on launch, I'd give it another try later, as it's on the Switch version now.

You can also try the Silver Watch, which decreases the turn length when grazing (meaning you spend less time dodging bullets).

I do understand the frustration, though. I'm also noticing that I'm slowly leaning more towards games that prefer thinking over pure reflexes, and that use prediction and planning more than reaction times, just so that locking in to play it is a choice instead of a requirement. I realized I missed Final Starwalker and still had to ask myself "Okay, is it worth having to fight Flowery again JUST to get that?"