I think the argument that others haven't strengthened enough doesn't really matter as long as PSG has the same squad that won the treble last season and won Ligue 1 several years in a row before that. It seems obvious to me that they will dominate. And they will certainly perform well in the Champions League too, given their overall form.
If other teams don't have the same quality of players as PSG, then I believe it will be difficult to break PSG's dominance in the next few seasons. This isn't because they won the Champions League last season, but because the quality of the players they have is far superior compared to other teams currently. PSG's strength is also much stronger now because overall, after winning the Champions League, they will be even more motivated.
But what's a little more difficult is how PSG can defend their Champions League title because next season's competition will be much tougher, with other teams also making changes to strengthen their squads by bringing in players they need.
PSG is very strong in Ligue 1, which is why many people say they will win the trophy again even though the league hasn't even started yet. But if you remember when Leverkusen won the Bundesliga, who would have thought they would break Bayern Munich's decade-long dominance? Even though Leverkusen's squad was mediocre at the time, they were able to compete with Munich. This could also happen in Ligue 1.
While PSG's dominance currently seems unbreakable, who knows, Monaco could spring a surprise next season, especially with the improved squad depth, especially with the arrivals of Paul Pogba and Ansu Fati. So, even though PSG is too strong to beat, we should still have a little hope for other teams who might be able to win the title.