I think Clan Wars need a complete rework because everyone knows the L2W strategy and exploits it and matchups are often unfair. The clans at the top of clan wars should be clans with the best players regardless of card levels.
My suggestion is that clan wars need to be reworked to the way tournaments are. Every week the first 3 days are training days and then the next 4 days will be a tournament which could be normal deck,no evo deck, one evo decks, 2 evo decks, classic decks, mega draft, double elixir, infinite elixir, sudden death. The mechanic of 5 loses and you are out still remains. The overall clan score will be determined based on the sum of the overall position of all the players in the clan. The matchups will be with other players at the same number of wins given the first priority and players at same war league given second priority.
Players should not be able to leave/join clans during battle days and that should only be possible during training days. This solves the problem of clans having backup clans and cycling players here and there all the time
For it to be fair to clans that have worked so hard clans will hold their current war leagues but all clans in the league will be reset to the lowest possible trophies in the league. Which means all clan in 0-1k war trophies will be made 0, 1-2k will be made 1000 and so on