I think he'd do great in CL, but he needs more than just a good team, he needs a team good enough to also win it without him. Meaning he is not the difference-maker in CL anymore, just a regular top player with quite a few weaknesses at this age.
So, he's more past, not in comparison with normal good players, but in comparison with his prime level.
Unfortunately, in CL, speed, and intensity which are often correlated with 30+ years of age, are essential. As good as Messi is talent-wise, he can't beat multiple players in dribbling runs anymore. His magical dribbling became more Iniesta-like, still special, but more static and less powerful and dynamic.
And, as much as we like Messi's freekicks, passes, vision, etc., the main Messi-skill, the most special part of him was always his dribbling at full speed for me. Taking on 3-4-5 players at once and dropping them like flies, and not only players from Granada, Bilbao etc, but even the best defenders in the world. He lost that to a big degree over time, and it's not a criticism as it's normal with age.