Of course going to PSG would have being the best for him because he will have the chance to play in Champion League all the time but that does not mean that he will have the chance of winning UCL because when PSG had the players which are Messi, Mbappe and Neymar PSG was unable to win UCL. Only Khvicha Kvaratskhelia will not be able to make PSG win UCL. Napoli is a good club and maybe he wants to play under Conte and hope that Napoli will qualify for UCL next two seasons so that he can display his potential for another big club to buy him but not PSG.
I don't think so, now we shouldn't compare in the domestic league, that's not fair but compare the performance and achievements of the team in the Champions League in the last few seasons and it is clear that PSG is much better than Napoli so the decision to move to PSG is a step forward for development career Khvicha Kvaratskhelia.
Besides, Napoli under Conte won't necessarily be successful, so don't overdo it.