SigmasonicX
Member
Twilight claimed that breaking up any friendship could have resulted in doom for Equestria, and that what was important was the general level of friendship. Going from that, we get to the more metaphysical idea that there is some guiding force making sure that Equestria has exactly enough friendship magic to solve whatever problems come up. Thus, maybe with the main six not together, there was exactly enough magic to solve all but one threat, and with minor nudging, exactly which threat couldn't be stopped changed.
In the first alternate timeline, some group of friends was able to stop Nightmare Moon (but not cure her?), Discord, and Chrysalis, but Sombra was too much for the amount of friendship available in Equestria. In the Nightmare Moon timeline, despite the eternal night, some groups of friends were able to stop Discord and the others, but failed to overthrow Nightmare Moon.
So who knows, maybe if Starlight went back in time to stop Lyra and Bon Bon from meeting, the main six wouldn't have been able to beat Tirek, since their Rainbow Power just wouldn't have been strong enough.
In the first alternate timeline, some group of friends was able to stop Nightmare Moon (but not cure her?), Discord, and Chrysalis, but Sombra was too much for the amount of friendship available in Equestria. In the Nightmare Moon timeline, despite the eternal night, some groups of friends were able to stop Discord and the others, but failed to overthrow Nightmare Moon.
So who knows, maybe if Starlight went back in time to stop Lyra and Bon Bon from meeting, the main six wouldn't have been able to beat Tirek, since their Rainbow Power just wouldn't have been strong enough.