We know this game is definitely no pushover. Especially doing all Arcade runs. So game features a Slow mode where you hold down said button to slow time. So instead of holding it down its better to tap it instead. It makes it last longer. For instence i beat Arcade easy on first try. Also did normal a few rounds after. I used only Dual pistols and "White" weapon. That weapon is the key to take out bosses very fast. However its dependent on your rank. So your job is to get S rank and switch to said weapon after.
All credit goes to @Kyoiceberg_ for telling me about this.
You can check my run on Normal Arcade for demonstration.
Arcade Mode Hard
And finally very hard