I'd actually like to add, that ever since Skyward Sword decided to drop that dumb bombshell on us, I was sort of always under the impression that there was some sort of active intention of "creating" the perfect host for Demise's hatred. Twinrova being Ganondorf's surrogate (I'm not really gonna elaborate on how that can be interpreted because either idea in that regard could work, I suppose), kind of suggests there was some carefully thought out selection in corrupting him through his very nature. That is, of course, if they really were associated with the tribe of evil. His possession of magic was likely deliberate on behalf of that party, though. But we don't get to see this stuff so that's my shot in the dark anyway.
What really gets to me about the whole "Twinrova is a surrogate" is that it's literally two witch twins who can fuse into one, so are they each carrying Ganondorf? Or is it only when they Meld together? I'd say That the G-man was a careful crafting of theirs, they found out they were the big preggo then started using magic to manipulate him into becoming the vessel for Demises rage, then again maybe he was just born that way a child born of an individual who is dual personalitied and literally split down the middle, between fire n ice to boot is gonna have some major schisming of the soul as it is. In Wind Waker we even see a more
human side of him where he claims he covets hyrules wind and this is what led to his crusade.......which kinda points to him only becoming as bad as he became due to the corrupting influence of the Triforce of Power. No denying he sought more power. He already ruled the Gerudo he just got over greedy the bloody pig.
See, that's where it's a cop out though and I dislike the notion. If you know you are going to die in a specific battle, why not just neglect to engage in that battle? If he was omnipresent surely he could do better, which makes me think he didn't literally conquer time.
Paradox issues, the entirety of SS is a big ole paradox, if demise is dead in the past how can he exist to threaten the future which is what sets ghirahim to take zelda from skyloft and initiate the whole thing. If Demise knows he dies in that fight and then doesn't go he no longer knows if he dies in that fight and therefore goes to that fight and so on it becomes a loop. I'd imagine that there'd be some uncertainty
right at the very edge of that foresight............ Or maybe he knew he'd one day return and so went into battle knowing that he'd become truly "immortal" forever reborn, if so he'd willingly go into that fight knowing he'd die but being able to return and in some ways more of a "match" for Link granted we don't actually see anything conclusive til OOT where lets face it Ganondorf actually succeeds at Demise's goal of conquering the land.