Simple fix to alliance hoping for AW seasons
All you need to do is set war ratings at end of season based on where alliances rank. Yes some thought needs to go into what decay to apply as you move down ratings but this will strip shell alliances of their war rating and probably at the same time, allow higher rated alliances to find matches quicker since more would be in range.
Main issue with this is if an alliance for some reason wants to take season off. However, if they are decently ranked they can do 2 BG wars or 2 wars a week to still place probably in the gold which means they effectively need to use the next season to work themselves back up some and then following season back to competitive
One minor adjustment to this for the scenario I brought up is have a minimum war rating given at start of new season based on prestige - this needs to be low enough that higher prestige alliances aren’t placed back into the top but high enough that you aren’t climbing the full mountain again - maybe t1-2 (in terms of prestige not war rating) Given t4 war rating, t3 prestige to t5 war rating etc. if alliance actual rating is higher there is no adjustment