On that...
My problem with the childhood justifications is that they add little. They already used it for Vauthry and Livia, and it can only add so much and doesn't fundamentally shift the blame, other than serving as an excuse. One which is incapable of really doing much to colour his modus operandi. He killed his father - and the only reason was to prevent him from getting in his way in hunting you, and not for any perceived grievances against him. Plus we're just assuming he was a negligent father. However, that's besides the point. Those kind of justifications won't get much further than that, and with Zenos now into his adulthood, it's not like he'll just "see the light". Doesn't work that way with psychos.
It's more that his encounters with us, and just about everyone else, have been, as others put it, "one note" - and like Theodric said, he's not even that true to his word. With other antagonists, like the Empire, the Ascians, and others besides, there's at least lots of different ways they can manifest the pursuit of their agendas and deeper reasons behind them. As things stand, even Vauthry may end up being a better fleshed out (no puns intended) character than the princeling.
Again, given his mania with pursuing you, it makes sense that it would be he who would try hijack the two Crystals like that... let's just hope they find a way to improve how engaging he is as a character. I too would prefer he did not outlast Elidibus, yet SE do seem to have some Sephiroth-type nemesis story in mind for Zenos.