I like the idea of a "classic" timeline that is separate from the modern games, but I'm not sanguine with really attributing it to in game events. It seems to be more a product of Nintendo just wanting to reboot the series from OOT.

On the other hand, this kind of reinterpretation based on the wacky the plot-hole-riddled timetravel in Zelda is good clean fun, and I like reading it. I had a timeline I made up under a similar concept, even though I don't think it matches up with Nintendo's plans in any way.

For normal timeline nitpicking, the idea of LTTP branching off of the child timeline via MM doesn't sit well with me, because the plot of the Adult timeline matches up with LTTP. Not to suggest your reasoning couldn't apply, there is clearly a lot of wiggle room with a flexible interpretation of timetravel.