It didn't work, so in hingsight it was a wrong decision.
But, at the time it seemed like a no-brainer and a sensible move but given how it did and would effect other things, it was not a prudent buy. It also massively changed the expectation and the talk around the club. If you listened to what was said prior, they reckoned they had the 3rd/4th best squad in the league, so a top 4 finish was reasonable, signing a Ronaldo upped the pressure to be win the league. The club buckled under that expectation and the squad was unbalanced by the changes, which lead to disaster.
Even now, if someone offered you Messi, you'd probably take it, even though objectively it's a terrible idea.