Yea, whoever wins the Champions League is always considered as favorite in the next season. A lot of people will always say this, after it has been proven wrong in the last four consecutive seasons. I don't see PSG as favorite next season in UCL because this is not Ligue 1, and we have some strong clubs that will stop them from defending the title successfully.
Defending the title is more difficult, especially since we are talking about the UCL trophy, where this competition is filled with giant teams in the top leagues, only one team has successfully defended this title and that is Real Madrid. PSG is still considered a favorite and may be able to maintain what has been obtained but it is not guaranteed. Madrid, Liverpool, Man City and Bayern Munich have made improvements so that next season the fight will be even more difficult for PSG, including Barcelona with Hansi Flick of course will try to win this title as a top priority.
Those clubs they you mentioned above can be called favorite too, because they have all won UCL in thw past and would love to win it again. PSG will be carried away with anxiety and they'll not be able to put in much efforts like they did this season before winning the league. Don't forget that PSG has been fighting tirelessly so see hoa they can win UCL and it cams to pass. I believe another team will fight to win UCL next season