I don't think that the CPU power is better but I think the CPU should be more efficient. Together with the bigger battery that should give us an outstanding operation time.

Design is better. But that's a matter of taste.

Beeing thicker it allows me to hold it save in my hands without a cover. The x was to thin in my opinion.

Screen is slightly larger, boarders are thinner. So having a bigger screen without making the phone larger is an advantage.

Bluetooth isn't good on X so hopefully that gets better with XA2.

XA2 is getting Android 8, X probably just 7.

Faster LTE Standard Cat 12/13 vs. Cat 6.

So all together, the only real technical reason for a switch in my opinion is the operation time. There are some "nice to haves", but nothing what changes to much.