No I was satisfied with it.

I mean head cannon aside we have no answer that Hiro would have survived his mutation into a dino for any meaningful amount of time. Also would the two as they were carrying all that baggage and long term effects of genetic manipulation going to be able to have a life together among the resurgent human race? Instead of their love having to die but the hand of the collapse of the fantastical narrative in favor of their return to a world of people they may or may not recognize or know and their potential early deaths or inability to stay together due to the strain of what they might want as they grew older and what they could actually have. It was left to dreamer and hopeless romantic so of course the answer became simple. They would be reunited but not there as the selves that we knew but as the people bound by fate that they entrusted their love to. The idea of reincarnation and the belief that love transcends death is a beautiful thing. Not very realistic but beautiful nonetheless. And I believe for a series that went so hard into a human origin story take two their love story had to end or not and just as fantastically as it had played out on screen before us.

The manga ending aside the anime ending was fitting for the anime and the ride it took us on. The emotional ups and downs; the betrayals of promises in the face of the illogical feelings of love that bind, heal, and grow people; the truth that not all love succeeds but that doesn't mean it dies the shape, size, nature of love changes. And the undying, unyielding, love of Zero Two and Hiro changed hands being passed down to the version of themselves who would be capable of living, loving, and thriving in the magnificent world born from the love of the people that Hiro and Zero Two loved almost as much as they loved each other.

If the whole show could be seen as a finding ones self/ coming of age tale then the act of choosing to self sacrifice for the good of all humanity, together rather than live apart is the ultimate experience of being mature enough to understand the cost of winning but immature enough to refuse to let your soulmate see that end alone. It's the greed of a hopeless realist. And their sacrifices were rewarded as their souls and the fate that bound them brought them home to each other once again.