Think of it as having enough money in the bank before you move to your dream location. You can make money in all locations, and some will require more money to go from one place to another.
In that case, the money overhead would be the talent disparity between you and competition (Or output, instead of talent.) Without getting into too much economy, one would need more money the weaker the currency is, and some places might have close to equal values.
Thats roughly how I'd rank these leagues:
For junior leagues that are not major, (No CHL, and Id say USHL tip-toes here), you'd need to be the best player in the league to make the jump right away, and even then I don't think you could. I can't really think of a player going from USHL, AJHL, BCHL, J20 or U20 Liiga and making the NHL, but the talent level is weaker and rarer.
For junior majors (USHL tip-toed and CHL), you'd need to be one of the best players... Think Suzuki in his final year, Guhle, Xhekaj vs say Mailloux, Barron, Davidson and Mesar.
For NCAA, you'd need to be at a similar level to CHL, but the league is slightly better than average CHL, so I rank it higher. Think of Makar, Fox, Caufield vs Harris, Struble, etc. Of course, there's always a case by case, and especially when it comes to players with big asterisks. Size and speed are the biggest ones, sometimes the jump is just too big for small players, like Farrell.
Then there's the euro pro leagues that would mostly all rank similarly-ish between NCAA and AHL. Slovakia, DEL, Extraliga, NL, Liiga, SHL and KHL.
Then there's AHL.
The further up the list you are, the better player you need to be in your respective league. In Slafkovsky's case, the jump generally requires you to be the best player on your team to make an impact right away in the NHL and to be able to keep learning at the rate you should learn.
Examples:
Rantanen was the best player on his team, then went to AHL and broke records and then started in the NHL. He never had "adapt" his play style, he learned to impose his playstyle on the NHL.
Hintz was the same, even if he took longer.
Teravainen followed the same route, but had a hard time to impose his playstyle in the NHL, he adapted in other ways. Size and skating both played a role in this.
Barkov and Heiskanen were both elite prospects coming out of their Liiga season, they dominated there and were good enough and had a clear defined play style that allowed them to have success right away.