For me Durante had more than one opportunity to enact his plan. Especially if it was mostly just for a chance to rejoin the great flow. He and the others could have gone through the gate Azdaja came on in through five thousand years ago. Heck I don't remember if those on the Void Ark or the other parts of the Mach raid that had the void coffins were brought over whole sale or not. If it took him over ten thousand years to get to the point where he and the others were sick of not being able to die then that is on him. Or if it only took them that long to come up with the plan then again that is on them. Which for me is why I have little sympathy for him. Don't see him in the same light as Emet-Selch.
The rejoinings couldn't be rushed or you'd end up with another 13th on your hands. There's only so much trauma you can deal to the Source before you cause it to try and absorb a shard that's not been prepared for a rejoining. Meanwhile Durante and crew could have sweet talked various people to allow them to come over wholesale. The Allagans and Machi were greedy enough.