Libby is phenomenal. For 19 years of age he plays with maturity beyond his years. His red card v Sydney was shocking but he'll learn so much from it. Doubt you'll see a rash challenge like that again for a while. Hardly puts a foot wrong in defense and is a revelation going forward in attack.
Totally different players and positions, but in terms of consistency, reliability and value, I reckon Libby is worth more than Singh. The rate hes going Bayern et al will be knocking on Phoenix HQ's door in January.
Libby has a great engine and can get up and down the flank the entire game, is naturally left-footed with good delivery, and has great willingness to go forward and win 1-on-1 match ups. That skillset is very sought after in Europe, because it's hard to find left-footed players who bring all the rest of it along too. Libby still has some way to go on the defensive side of things, especially as a full-back and at higher levels of the game, but at his age, that's not going to stop people from wanting to bring him in.
Think that there is a decent chance that he leaves in January, and I'd say it's almost certain that this will be his last season at the club.