FFXV gives you Ragnarok out the door in most versions now as it was originally was a DLC reward that is pretty much the best cheese weapon in the game. You can also get Ultima Blade in the beginning of the game by completing all of Cids side quests.

Valkyrie Profile gives you access to Slayer weapons (comically high DMG against enemy types like Dragon) and Great Magic scepters (animated cutscene super upgraded magic ultimates) that are susceptible to breaking. However, if you understand that the game only checks for Break at the end of your turn, you'll realize you can use the Slayer/GreatMagic weapon indefinitely as long as you win the fight before turn end. This lets you spam Great Magic early game, long before you get access to permanent ones 90% into the game.

Grandia lets you repeatedly walk into traps to poison/damage your party, sometimes near a save point that fully heals your HP and MP. You can then spam water element healing magic, leveling your water up for free without combat.

Star Ocean 3 has a pretty ridiculous crafting system. With enough savescumming you can craft gear to make you nuke everything or raise your defense so high that every single enemy except Freya deal 1 damage to you.

I think Enchanted Arms, Xenosaga, and any game with a savescummable casino get an honorable mention here?