so it depends what you define as success, but if you want players capable of performing at the level of a club like Inter, then at just a quick pass from our team of starters+quality bench:
Handanovic Serie B 1 season, the rest Serie A except aged 18/19 (Slovenia 2nd league for 11 games)
De Vrij top flight football since he was aged 17
Ranocchia 1 season of Serie C aged 19, 1 season of Serie B after, A the rest
Dalbert is a bit of an anomaly - 1 season of 2nd league in Brazil aged 21, but then moved to top flight after.
Di Marco - 1 season (12 games) in Serie B, aged 18/19 I think
Dambro 1 full first team season at Serie C level, B for 3 of years after, then A.
Darmian - A/B his entire career. 2 seasons total of Serie B, aged 20 and 21/22
Skriniar - top flight since he was 17
Bastoni - top flight since 17
Gagliardini - Serie B till 22, but I'd argue if he deserves to be on this list
Vecino - top flight since a kid
Sensi - Lega Pro until 19, one season of B, then A. But basically always as a starter.
Perisic - top flight since 19
Hakan - top flight since 19
Barella - 1 season of Serie B aged 18, the rest Serie A
Eriksen - top flight since 17, as a starter
Nainggolan had 1.5 seasons of Serie B as a starter until aged 19 I think, then Serie A ever since
Brozovic - Croatian first league since he was 18/19
Lukaku - top flight since 16
Lautaro - top flight since 18
Sanchez - top flight since 17
pretty much by virute of even playing at Serie C level, the probability of you 'making it' is VERY low. And that's as a regular starter. If you do play in the lower leagues, you get like 1 maybe 2 seasons at best (statistically) to assert your quality and move to the top flight - even Verratti had 2 seasons of Serie B (aged 18 and 19) before moving to a big club.
Like I said, a few things:
1 - Most pros will never ply lower league football
2 - If you arent a regular starter by the time you're 19/20 in the top flight, you're very unlikely to make it at a top level
3 - If you aren't in the first team squad aged 18, you're unlikely to make it
That's why B teams are a waste. Because, by that age, the probability of making it vs not making it is ~95% decided anyway. And thats why our youth transfer strategies never work out. We sign all these 18 year olds, they never go anywhere. Because its too late in their development cycles.
If I look t the 22 who staarted in the CL final
Ederson top flight except for an adaptation 4 matches in Benfica B
Walker - 2 seasons on loan in the championship (as a starter,) then first team regular aged 21/22
Stones - one breakthrough season in the championship aged 18, then Everton
Dias - Benfica B for 2 seasons until age 20, then top flight ever since (Benfica B were 2nd league)
Zinchenko, top flight
Bernado Silva - breakthrough season was aged 19
I'm gonna stop here but think you get the point. (couldnt be fucked clicking through everyone else tbh
)
It's unfortunate, but the stats dont lie. Inter needs to cut harder. If we had a B team, I would allow one development season for the kids at that level, and if they dont display A/B level qualities, they dont make the cut. You'll inevitably lose a couple of gems (But very rare), but it gets us away from the disaster of a youth sector we have now where we dont produce jack shit.
Notice all of our stars have been first team, top flight regulars since they were aged 17/18 basically.