It's just coaches and teams find it harder to complement Messi's qualities than it is for Ronaldo's. Ronaldo's strengths are pretty much aerial abilities and channeling through counter attacks while for Messi you need to know how to link up well and create a multitude of spaces for him to be extremely lethal (Pep figured it out). Obviously both styles have their various disadvantages and advantages. It doesnt necessarily mean Messi isnt as effective as Ronaldo, surely there's some off forms now and then, probably due to fatigue or motivation like Ronaldo has at the start of the season as compared to Messi's end of the season.
One thing for sure at this age, Messi needs to be well rested and preserved if you want him to perform till the end of the campaign because he usually fizzles out.
They're both Ronaldo and Messi for a reason, and far too many factors to simply conclude one is a bigger player than the other. For all you know, Ronaldo could simply go missing again the next match like he did in the CL final except his teammates did step up. I still believe both are very great players and in tournaments like that the team still has to contribute to attain the ultimate trophy. They both cannot do it alone all the time.