I'm no sure he will be a decent striker in UCL. The match won't be as easy as in La Liga. If he has no much experience in UCL, it is difficult to score many goals in this competition. If Real Madrid dreams for UCL title in the next season, they should sign an experienced striker in UCL. Real Madrid needs a striker like Mbappe, Osimhen, or Harry Kane. They are very experienced in UCL and they are productive enough so far.
There are still much rumors about Real Madrid, I heard that they are getting closer to sign Mbappe lately. I know Perez already stated to sign Mbappe next year, but he may change his mind after looking at Real Madrid current squad. Mbappe's contract is only 1 year left, his price should be lower that last year. Ideallly, Mbappe's transfer fee is below €200m now. So, Real Madrid has a chance to sign him in current transfer window.
As much as I would like Real Madrid to sign Mbappe this season, I think the €200M price tag is too much. PSG should be reasonable and lower their asking price. I don't think Real Madrid is ready to splash such an amount on him based on the fact that he has less than a year on his contract. Perez might strike a personal agreement with him and have him for free next season and if such agreement is reached, then it rules out the possibility of bringing in Harry Kane or Victor Osimhen to the Bernabeu. Joselu and the others can hold the frontline pending on his arrival next season.
But why is it too much? Neymar cost €222M and he didn't make PSG a much better team. But if you see the potential that could be made use of when Mbappe goes to Real Madrid, I would try to sign him now. They will be selling merch all around the world and the buzz that this creates lets Real Madrid shine in popularity once again. I think the Mbappe to Real Madrid transfer is about 5 times as interesting and important as the Neymar to PSG transfer. Mbappe is going to take the lead in world soccer as an individual but also with his teams.If everything works out the €200M will even look modest in 10 years from now.
You should be aware that today players are not only bought for their playing value, but also for their marketing value.
How much did PSG's earnings increase just from the increased sales of their jerseys with the names of Mbappe, Neymar and Messi? It is about hundreds of millions of euros, and with that they already paid off their contracts with PSG.
Also, the club gained more fans and followers on social networks, which also increases the value of the club in terms of marketing.
Today's clubs adapt to the market and sponsors and have very good marketing strategies, and are aware of the importance of brand building.
As for the contribution of individual players to the results and successes of the club, that is a completely different question and obviously in that segment of business, PSG did not do a good job, unlike Manchester City.