Here is Lewandowski's stats so far in the La Liga this season.
The source: https://www.sofascore.com/player/robert-lewandowski/41789Having an average of nearly 1.00 goals per game isn't bad at all. Yeah it isn't perfect performance considering the general stats but at least better than last season.

When it comes to setting the bar at Messi and Ronaldo's level, it is really not an easy job for any player in today's football I think. Messi and Ronaldo made us get used to scoring at least 50-60 goals in one season but those were really extraordinary stats. If Mbappe manages to reach that level he will surely be a legend just like them.

I would have to accept that Lewandowski is not performing badly in the La Liga this season. At his age, I expected that his performance would have reduced to a large extent, but this has not been the case. I suspect that the Polish international takes his training seriously and lives a healthy lifestyle. Most players of his age have lost form and gone on retirement but he has kept improving. Messi and Ronaldo are in the highest class of players. Mbappe might get to that level if he keeps improving.