It should be the same result on XCP-ng Center: it uses RRDs files stored on the host.
Why do you continue to talk about the after the reboot? You mean after the upgrade, right? RRDs are preserved after a reboot
If you do a yum update, those stats should be in theory preserved. If it's not the case, try to diagnose why, by comparing behavior between XCP-ng Center and XO. If it's not the same, then it's a client issue. If it's the same, then it means a version upgrade (yum or ISO) won't preserve RRDs.
If you really want long terms stats for "real production" usage on long term, I strongly suggest that you think to store them in a real time series database, like Prometheus or so.