You're correct about the stat but the competitiveness of the league itself is irrelevant, I think. The Albanian league might be very competitive (I don't know if it is, it's just an example) but I still wouldn't consider someone who had never managed elsewhere.
In very poor leagues, continental competitions are often a good indication of how a manager is doing. When you drop down to a certain level, one good player is often enough to make a difference but such teams get found out at continental level.
Then again, it's going to be a throw of the dice, whoever it is. For what it's worth, I read some good things about Postecoglou when he was managing Australia. But there's so much more than the technical side to succeed at any club, let alone a club like Spurs. We saw that with Conte.
