I would say that if Germany would start with their very best team, they would be better than the best team of GB, mainly because of the stronger field events. The same goes for Poland.
I once made a ranking based on the best results per country per event in 2018 according to the website of European Athletics, where I converted everything to points. Without the relays, the results would be as follows:
The reason France is so low is because they don't have a lot of athletes that scored exceptional results in 2018. However, they have a lot of depth in their national selection, so when their best athlete doesn't take part, they can easily be replaced by a number 2 or 3 who is of a very similar level. The Netherlands on the other hand is dependent on a small number of athletes, such as Sifan Hassan and Dafne Schippers. If they don't take part or if they're not in great shape, we would lose so many points that we would definitely finish dead last in any Super League. Same goes for Turkey and Sweden, and Italy to a lesser extend.
Based on that ranking, not including Russia and having each country participate with their best possible team, I would love to see the following leagues.
Super League: ESP, FRA, GBR, GER, ITA, NED, POL, SWE
First League: BEL, BLR, CZE, FIN, GRE, HUN, NOR, POR, ROU, SUI, TUR, UKR
Second League: AUT, BUL, CRO, CYP, DEN, IRL, ISR, LAT, LTU, SLO, SRB, SVK
Third League: ALB, AND, ARM, AZE, BIH, EST, GEO, GIB, ISL, LUX, MDA, MKD, MLT, MNE, MON, SMR