It’s clear that Joselu is no match for Mbappe; he was literally rented as a temporary option. By the way, this is an interesting turn in his career: before Real Madrid he did not have any titles at the club level, but now he already has the Spanish Cup + Super Cup and this season he will at least become the champion of La Liga. I don’t know if he will be able to return to Espanyol after such a takeoff. Considering that he is already 33 years old, it is likely that he will simply end his career when he leaves Real Madrid.
If I'm not mistaken, around 2010 he had already experienced the same stage as Cristiano Ronaldo and other players at Real Madrid, but unfortunately his career didn't last much longer and he had to leave Real Madrid to continue his career with various teams. Until finally, at the beginning of this season, Joselu returned to Real Madrid but was still on loan from Espanyol and as you said he was only a temporary striker while the club leaders determined the right replacement after Benzema.
It's not easy because from now on his position is starting to be threatened by the presence of several young players and as an older person it will be very difficult for Joselu to compete. But at least he has won several titles with Real Madrid and I think he will still be happy even though he will be disappointed that the club will not make his contract clause permanent from Espanyol. But what is clear is that Joselu still has the opportunity to add to his trophy this season and that is the Champions League title which all the players really want.
Yes, he played a couple of meaningless games for Real and even scored two goals, but it is obvious that compared to Ronaldo and Benzema, he did not have a single chance of appearing on the field at least somewhat regularly.
Overall a pretty interesting player, I see that he played in as many as 11 clubs and his longest stay in a club was 3 years in Alaves. I once read an interview with him after a game for Real when he scored a goal and was very happy about it and at the same time criticized himself for a bunch of wasted moments, and since then I have felt sympathy for him.