Anyone, and I mean anyone, can beat this game if they're willing to keep at it. And I'm not talking about the long term, either.
There are three things about Zeroigar's gameplay that I think non-Japanese players are prone to missing:
1. The points you earn are actually like experience points, and your ship levels up frequently throughout the game. That's what that starry black-background screen is all about. Every time you level up, you gain stronger shot power, more armor capacity, and more subweapon ammo capacity. Your level never goes down. If you keep playing indefinitely, you will level up until you are at god-like strength.
2. The powerups you collect during the stages give you more firepower in a sense, but this is different from the "Power" variable that goes up when you gain a level. The powerups you collect make you fire more bullets, but the "Power" stat that goes up with your level determines the strength of each individual bullet fired. If you're at Level 10, you're almost guaranteed to be stronger than you were at Level 1 even if you aren't firing as many bullets.
3. Use the Wind Cannon subweapon. Someone posted a clever walkthrough of Lords of Thunder that just said "Use the Earth Armor". This is similar. Anytime the enemies are getting thick, press that subweapon button. Just trust me, it works wonders. It doesn't drain very quickly, either.
So the moral of the story is, keep playing, because you will level up and get stronger, and just losing a bit of power because you got hit/died actually doesn't mean as much as you think it does.