This is to offer a thread aside from the special league threads to discuss those inter-league relations. I begin with my current personal view and compare it with the last published European Cups ranking:
2. Russia and Italy
4. Poland and Germany
6. France and Romania
It is important, to keep several facts in mind: the broadth of quality of a league vastly differs, i.e. relation of best to weakest teams in a league can be an huge or a small difference. My proposal above is difficult in this regard, because in Russia the differences in super league are much bigger from top to small teams than in Italian A1 for example, the same holds true of Poland and Germany (the first has much bigger quality differences). And second the European Cups ranking, unluckily only available in a dated version publicly, one year older than the latest European Cups results (ranking valid for 2018 cups includes results from 2014 to 2016 cups, not yet the latest 2017 results), contains three years, in which some leagues improved or decreased considerably (the last applies especially to Azeri superleague now, the French league suffers in ranking from the heavy loss of quality of RC Cannes in the last few years) and also considers only the best CL results with the biggest influence, the best CEV cup results with smaller, but still considerable influence and the best Challenge Cup results with generally small influence on the ranking. So leages with one outstanding top team can be ranked higher than the league in its broadth would justify, so the Swiss national league is better ranked due to strong results of Volero Zürich currently (all the time CL Playoff-6). Here are the top spots of this "current" European ranking for comparison:
Due to the massive weaking of the Baku clubs and questionable, whether the always small superleague there will continue to exist, this entry 4. is not conforming to reality any more and a remainder of times, when they hired world class players with much money, what has essentially ceased. After rebuilding their roster with less many as before, Volero Zürich has to prove, if they can defend that Swiss ranking anymore...
Italy not always sent teams to CEV cup and made that way less points as they would have made when doing so, this explains mainly there weak ranking. Germany faces now a weakening because no of the clubs directly respective for qualificiation eligibe takes part in 2018 CL respective qualification for it, so Schwerin, Stuttgart and Dresden can only earn best result points from CEV cup in 2018 season (likely semi final).
From 4. place leagues for example Poland club Chemik Police is the strongest obviously, but relation of best German clubs Schwerin, Stuttgart and Dresden (and others) to Grot Budowlani Lodz and DevelopRes Rzeszow for example is to be clarified, unluckiley there will be no comparison in next time it seems.