Now even I wouldn't pretend Patrick = Crosby.
Patrick's struggles are a combination of lost time due to injury (especially summer workouts and training), lack of physical maturity (not strong enough for the style of game he should play, similar to Couts), and lack of confidence, due to inexperience and age. But at worst he should be a 35-40 ES scorer with above average defense, good luck finding a better 2C outside of Duchene. He has the entire skill package, he may not have an outstanding attribute but also lacks any glaring flaw, above average skater, shot, size, work ethic, hockey IQ.
Frost is as close to a sure thing as you'll find outside the top five. That extra year in juniors, like it did for Barzal, gives him a big edge going to the NHL, time to physically mature and polish his game. He dominated the CHL as a 19 year old, whereas the majority of top CHL scorers were 20+ years old. No one is a sure thing, but you don't get much closer than Frost.
Farabee simply did everything you'd want in his D+1 season, shined at the WJC-20, adjusted to playing against older players in college and finished his freshman year as a dominant NCAA scorer. While they might start him in the AHL, my bet is he'll make the NHL team, he's clearly more advanced than TK at the same age.
If you want to win a Cup, you have to go with young talent like these three and let them grow on the job.
Players like Ratcliffe, Rubtsov, Kase, etc. are different, they have talent, but need to polish their game, get stronger (healthier) etc.
When they're ready, you'll know, because you'll watch the Phantoms and see them look like men among boys.
Players like Bunnaman, Vorobyev, Twarynski, etc. will need time to overcome their flaws, the question will be whether they learn to compensate and become NHL players or flatline.