Actually it's only humanly feasable to defeat the Dark Aeons and Penance in FFX using the Ultimate Weapons, I can't even fathom to defeat them while doing 1/10 of the damage, especially the Penance battle.
As easy as it was, Penance had always a small chance to do a one hit kill attack, so the battle dragging 10x longer would only increment those chances over time.
Current PC Build
CPU - i7 8700K 3.7 GHz (4.7 GHz turbo) 6 cores OC'd to 5.2 GHz with Watercooling (Hydro Series H110i) | MB - Gigabyte Z370 HD3P ATX | Gigabyte GTX 1080ti Gaming OC BLACK 11G (1657 MHz Boost Core / 11010 MHz Memory) | RAM - Corsair DIMM 32GB DDR4, 2400 MHz | PSU - Corsair CX650M (80+ Bronze) 650W | Audio - Asus Essence STX II 7.1 | Monitor - Samsung U28E590D 4K UHD, Freesync, 1 ms, 60 Hz, 28"
