Lewandowski in Barcelona plays the role of a senior who is guiding young players to gain trust and motivation, while the goal contribution is just a bonus that he deserves. Not many players at his age are now able to score many goals, let alone become the top scorer in La Liga for a while and followed by Mbappe behind him. Even if in the end Mbappe is able to catch up, it still won't disappoint Lewandowski. Because no matter what his age and era are different from Mbappe.
Lewandowski becomes a mentor for much younger players at Barcelona because his experience can provide a little ability in the team when facing pressure in big matches. At an age that is no longer young, scoring goals like him is something quite extraordinary and I agree with you because even if Mbappe later surpasses Lewandowski's number of goals, it will not be too disappointing because Mbappe is still quite young and still quite productive.