Shelley is a good young player, certainly not ready for the jump to senior level, and basically until they make that jump it's not a guarantee they will ever make the grade.
Many factors to consider especially when it comes to PGs, they are the engines of a team, look at Mitchell, Harrower and any of the really top PGs, not only are they good players they are good decision makers, smart and organised, they are you on court leaders/coaches, they may be fine in their junior levels, as the rest of their team mates are on the same maturity wavelength, but at senior level your dealing with adults not kids
Many of those names will never make that jump for any number of reasons , from ability to communicate, to gaining respect so their team mates listen, to being a great reader of the game, knowing all positions and what their team mates strengths and weaknesses are, and being able to take control of not only tempo but also at crunch time.
Add all these to being able to p,at both ends of the court and a good PG is not that easy to come by hence why once found they are not quickly replaced unlike other positions.
Bit like a good centre, few and far between, but you 2/3/4 positions are the ones who change frequently and usually depending on a coaches personal preferences.
Over the next few years they will hopefully sort the chaff from the wheat, then you can revisit all those obscure names somevare throwing up and see how on the money your were lol