Thomas was part of the British setup up from 15.The first three riders were older riders when they joined Sky. Only Geoghan Hart joined asa true neo pro - Sky does not have a good record at developing young talent.
Frome was a nothing rider going nowhere, signed purely because he had a British passport and was available as part of the Barlowwold out of work group. All his development was with Sky.
Even Wiggins was a Brailsford boy from a young age, drifting through French teams to top up his wages whilst winning gold medals. Yes he had one good year in 2009 before Sky existed . Even then Brailsford was most likely dragging him out of pubs, kicking him up the proverbial and convincing him he had the talent.