CC seems like a weird choice on Xerneas, especially with that set. The defense drops from CC contradict the whole point of running EVs on it, making it really easy to revenge kill with priority. Even if you do wanna run CC, you should change the nature to one which lowers either of the defenses and invest enough EVs into attack to outdamage Soft Boiled recovery -- that is, go for a hardcore offensive set (although I recommend you do not do this).
Its better to make a team around Geomancy Xerneas rather than make it the one-man-army, and provide as much team support as possible. You can alter a few things like running HP[Fire] for Ferrothorn or HP[Rock] for Ho-oh if your team takes care of whatever coverage you're missing out on (for example, if you run HP[Fire] then your team should take down Ho-oh before Neas comes in) but the whole point of a late game special sweeper shouldn't change.
If you're having trouble with Chansey, then its better to include mons in your teams which can take care of it. Marshadow and Tyranitar with Pursuit seem like good teammates (do note that I only play USUM AG, so I have no idea about their viability in NatDex AG, but you'll get the point I'm tryna make) since they can continuously chip it away and if you can pressure the opponents enough to prevent Soft Boiled, then its ggs wp.
Dugtrio also surprisingly makes a nice core with Neas (at least in USUM AG), taking care of 3 of the 4 best Neas checks - SpD NDM, Primal Groundon and Arceus-Poison. (https://pokepast.es/1f1d8b3abd114980
- A team I made with that core which was really good, USUM AG.)
Its better to make a team around GeoNeas taking care of its checks then to make an all around Neas set.
Edit: Should I turn this into an answer?