You are also relying on Messi staying injury free like Ronaldo. He is more injury prone than him currently and in his 30s he could be even worse. Ronaldo may also go to destroy the French league while Messi stays in a more competitive Spain.
Of course, but him becoming more injured in the future remains to be seen.
Injured or not, Messi scores just as many goals as Ronaldo despite being out for two months.
This discussion isn't about whether he will score more goals than Ronaldo or not, it is about, whether he'll continue to score 50+ goals per season for the foreseeable future and I say yes, absolutely.
Messi roughly gets a goal a game now. As he gets older he'll play deeper, whereas Ronaldo is more of a penalty box striker as he gets older. Also Penaldo plays every single minute of the season near enough whereas Messi gets some injuries.
Ronaldo will maintain his goal ratio for several years as he's become more of a goalscorer and more hungry for goals. It'll work in reverse for Messi.
If zlatan can bang in 40 a season in France Penaldo will be pushing 60 for that team.
Why does so many think he'll drop deeper and deeper with him getting older and older? He is already playing incredibly deep at times, but is still scoring like crazy, why should this change?
I think you might be thinking about it all wrong.
You see Ronaldo as this incredible physical specimen, scoring 50-60 goals each season because he is obsessed with scoring goals, when in reality, his obsession is his -and his team's downfall. His obsession with goals (keeping up with Messi) has lead him to become a one-dimensional player, who doesn't care about his team nor his teammates, he would much rather pick personal glory over the team's, because he loves being the sole person in the spotlight.
So you see him, being closer to goal as he gets older, well that is because he is one-dimensional, that doesn't mean he'll score more goals than Messi, it just means that he is one-dimensional. Messi will likely continue to play like this for the next 3-4 years, he is after all only turning 29 this summer and he will continue to score just as many goals as Ronaldo, depsite be being further from goal than him.
Everything points in that direction.