It all depends in how you view it. If you assume that all these timelines would happen anyway without conscious effort to create them on the part of the Shifters, I guess it makes everything rather moot.
But I generally figure that these timelines still had to be actively created by their participants in order to exist. Yes, multiverse theory posits that every possible outcome for a decision exists out there somewhere, but it doesn't necessarily mean that those decisions just 'happen'. Someone needs to make the decisions in order for the relevant timeline to be created. The real question is why do specific decisions get made?
It's like, if we stick a red door and a blue door in front of Zero, and he chooses to go through the red door....but I needed him to go through the blue door. It's all well and good to say there's a timeline out there where Zero chose the blue door, shrug my shoulders and leave it at that. But then *why* would he choose the blue door over the red door? It's all very well to just assume such a timeline exists, but
why does it exist? Does it exist purely because of the vagaries of random chance, or does it exist *because* I set out to engineer a chain of events that ultimately pushed Zero to choose the blue door?
It's a subtle distinction, but important I think.
...Which brings us back to interpreting the game. If you go with the 'everything is going to happen anyway, so meh' outlook, then everything in existence ends up becoming rather pointless. And we end up here:
Meanwhile if you assume a level of conscious interaction required to influence timelines, the plot turns out to be a work of genius. Within a single set of events,
Every necessary timeline is created.
The one that results in Delta's birth. The one that leads to the Radical-6 ending where Sigma and Phi develop their shifting powers. And of course the golden timeline. In terms of temporal structure, it may be the most brilliantly designed time travel plot I've ever seen.
...But that's only if you give weight to human decisions instead of deciding everything is pointless