Messi is still top 10 IMO. He only does poor compared to his past versions of himself. Only a few younger players are ahead of him. Most of these wonderkids running around still haven't even touched his diasterclass form
I guess it deoends whether we are talking in terms of ability or judging him by his performances this season. For instance, Neymar when fully fit might still be a top 25 player in the world but certainly wouldn't come close to making a list of top 25 performing players this season.
In terms of ability, you could make an argument for Messi still being top 10. I would probably have him around 25-30 although it is tough to judge since he was great 8-12 months ago and there seems to be big variability in his performance depending on the environment. If judging solely by his performances this season, then even top 50 would be very generous though.