If Zlatan would be aged 25, then Zlatan is my pick.
Without Messi, Barca wouldn't be built around Messi, and Barca's team could be built around Zlatan. So, Zlatan wouldn't fail here.
And teams built around younger Zlatan usually win all domestic championships.
About Champions league, Messi "messed up" a history in the last 10-15 years.
Without Messi and Cr7, if younger Zlatan played in Barca/Real for 5-8 years, he could win 2-3-4 CLs in that universe easily, imo.
On the other hand, Ney and Suarez would also be different players in that universe.
But my pick is Zlatan, since younger Zlatan is the only guy (except Messi and Cr7) who can turn matches into a one man show and decide them all by himself and who has a high leadership ability.
If someone will reply that Zlatan was poor in biggest matches, well he played for Juve, Inter and Psg for majority of his career.
What if he played for Barca for 10 years, and if we had, for example Neymar-Zlatan or Ronaldinho-Zlatan attack for 10 years (with Xavi-Iniesta behind them and a random expensive RW in our team)
I am quite sure that Zlatan wouldn't be a guy with poor stats in key CL matches in that universe.