The thing is that the a league is a good league and not miles away from the premier league, at that level the difference between a premier league player and an a league player comes down to small percentages. Half a step quicker, a fraction of a second faster at making a decision, releasing a pass sightly earlier, etc.
Compare that to the number of struggling pros or jouneymen from lower levels who have come the other way and done very well in the A League . Ifill probably top of that list
Plenty of a league players could almost do it but just lack in one or two areas.
I guess your definition of small differences and mine differ
This is also the nature of a salary capped league (and Ifill said this as well)- enormous levels of difference within teams. Whereas you'd expect a non-capped league's teams to be a bit more even in ability.
It's hard to say where and how players develop. Jedinak is a player who obviously kept developing. As did Kruse, though he's not been getting selected recently. I'd put Kruse and Langerak in the developed in the A-league category. Playing for that Leverkusen team is as good a level as being in the Premier League. Ditto Dortmund.