The two examples you gave are absolutely right, but not all the best players are like that. So I won't equate Osimhen with the two players you mentioned as examples, because there are also players who when they go to other big clubs become more famous with their good performances that never decrease or disappear. So don't just look at the bad examples, but try to see some good examples from other players so you can be a more accurate comparison for this.
You make a good point about avoiding making generalisations based on a handful of examples and taking into account the success stories of athletes moving on to big teams. Its critical to recognise that every player career is different and some players prosper and get greater reputation as a result of their performances at new teams. When evaluating a players adaptability it is also important to take into account the different playing styles and tempo of leagues like La Liga and the EPL. its wonderful for a player to succeed right away at a new club and crucial to understand that there is still potential for development and future success in their career.