I never finished the game but Sin was an eternal cycle. His spawn was damaged and killed but not him. NemeBro can explain it more. IIRC they tried to combine some Albhed tech weaponry with magic or something. All I know is that conventional weaponry doesn't work.
Sin was, for all intents and purposes, invincible to conventional weaponry.
Not only was it massive, with a fin that on its own dwarfed a very large ship, but its body was very durable, able to tank Al-Bhed weaponry that only pissed it off.
What also makes Sin very hard to fight is its Sinspawn, various kinds of monsters it spawns from its body to help defend it, it can create enough to have its own personal army.
How it was defeated, well, the party fought it, attacking its various body parts(arms, core, face, etc.) along with attacking it with a huge airship, which was probably the most technologically advanced thing in the games(weapons-wise, and with the obvious exception of Vegnagun), so they had an airship, a bunch of peoplez, and attacked its body. Oh, and they also were able to "calm" it during the fight using the "Hymn of the Fate" or something like that, a song which the current "host" for Sin, Jecht, used to wuvz.
Ganondorf would have no problem with the sinspawn. Sin's size would be a disadvantage due to ganon's teleporting. he could blast a whole or cut one into sin and attack from the inside
Was bored, so I felt like posting this. This is Sin's first appearance in the game, shielded by water that surrounds it, and levelings several large buildings.
Ganondorf isn't going to stop Sin outside or within. Sin is practically immortal and is capable of causing massive amounts of destruction. If Ganondorf manages to get inside, he's gonna deal with the final Aeon and Yu Yevon who can continually heal itself and cast Ultima over and over.