It's not as bad as it sounds, it's just very memorable when it does happen because it always catches you off guard, and technically you can build units to deal with the game's cheap shots if you spend enough time with Fusion. At least Persona doesn't have back attacks and enemy reinforcements, like the mainline games have. You haven't lived until you get accidentally back attacked and watch the enemies murder your party or defeat a hard group of enemies only for a freaking Aeon/Deity class demon show up afterwards as reinforcements to pummel your weakened party.

For the question, I don't mind RNG within reason. Like Del, I'm not a fan of super rare drops from super rare enemy shenanigans and I don't like randomized chests either. With that said, I'm not against spending some time to grind enemies for a particular drop within reason, and this is also why I generally like having thief type characters in RPGs to help. If their is a way to boost drop rates, I'm usually for it unless it's a requirement to make a 0.001% drop go up to 1%. At that point the developers can go screw themselves.

Where RNG does get a bit weird for me is in action games where bosses can go from being absolute nightmares to something manageable. Especially annoying in fighting games, where bosses tend to fluctuate between precognitive levels of combat to simply letting you use their face as a punching bag.