Mikey Moore became our youngest player at aged 16 last season, similar age to when Sam made his first team debut for Southampton
Its usually easier for good young players to get first team experience at a younger age at 'smaller' clubs (which is why loans by PL teams to lower league teams happen). But to make progress they usually need to leave the 'smaller club' and join the bigger club - not always an easy leap
Its also true that Sam came through the Spurs youth system at a time when Poch had killed off all loans and most first team playing experience, so with most first team pathways closed down there was less hope of young players getting through, followed by a short renaissance under Mourhino and then a complete freeze of youth development under Conte.
Spurs current crop coming through may show Spurs have learned their lesson and want to get youngsters through into the first team, so had Sam not walked he'd be in Spurs current crop competing to get Ange's eye for the first team.
But at time Sam left, certainly the right decision for him - and might have been the final nail in the coffin of not taking the youth system seriously enough at Spurs.