As regards track cycling and swimming, finally the italian federation are making investments in the structures and most of the athletes are now able to train also abroad. In athletics we are so strong that we are dominating the medal table.
The answer is simple: as a teenager undergoes growth and development, its "feelings" (meant as adaptation to technique and physical stress) becomes different and requires time to calibrate, while this is not true for people in the mid 20s, as Panziera and Codia. As regards all the other swimmers you said, Quadarella, Vergani, Cusinato, Miressi and Zofkova did very well in Budapest and in the short course european championship, this is just a confirmation. As regards the other, honestly I don't know very much about them in terms of their history and their previous best, so I'm not saying anything.
I don't know about Wellbrock or how it is written (by the way, is there a law in Germany that denies apostrophes in English words?), but how it is possible that a "kid" is now competing with the best in the world? (I'll answer for you: it is exactly what I told before regarding the others).
In the end, as regards the Italian to be considered as talent: Italian young athletes are among the best in the world, but our system doesn't really help who wants to be an athlete and then keep on doing other things.
PS: were you as suspicious as you now are with, for example, Laura Dahlmeier?