As a casual NBA fan and basically a totally ignorant international pro basketball fan, could someone explain a bit about the hierarchy or relative prestige/pay/quality of the leagues overseas?

I noticed that Johnathan Williams (a marginal NBA player) is now set to play in Israel. NWG obviously was playing in Greece. Kyle Wiltjer has bounced around for a few seasons.

Is there anything like a "#1 league" outside the NBA? If there is, why wouldn't a fringe NBA guy like Williams end up there?