Agreed. I hear this complaint frequently with the Jaguar version, but the fact is the game only lets you fire so fast. There's no reason to mash because half of your inputs won't actually be doing anything. Just tap at a moderate rate and your hands will never wear out.
It's not really the rate of fire for me, as it is just 25 years of blue-collar wear and tear in a job where I use my hands to grip heavy objects. My right thumb (the firing thumb) isn't really in shape anymore for that kind of abuse. It's not about being lazy, and it certainly isn't about cheating. Maybe some day people here will experience more what I'm talking about.
Zero 5, now that game is even worse, that has an extremely high rate of fire, and it's an awesome, awesome game, but I just can't play that anymore, at least until I can get a rapid fire pad somehow. Now, Tempest 2000 or Defender 2000? I can play those for hours, just hold the button down, easy. That up-n-down motion with Raiden I get thumb fatigue quick, I have to play the PS1 game nowadays, since it has a rapid fire option, plus readily available joystick setups.
On topic, Raiden is a must have game for the Jaguar. Great soundtrack.