Main advantage is for whatever the reason if a clan splits, they can then regain their friends and new ones by merging. would definately help new members being able to be in a clan fairlu soon on the game whereas now if you watch in global there are lots of new members struggling to join a clan or having to create their own clan
just to try to be able to partake in wars. Another advantage to stronger clans merging with baby clans could be the "mentoring effect". Everyone remembers being new in this game but by merging 2 clans, it opens up an entirely new avenue- one of teaching new members new skills and strategies by example from older clans.
By averaging out the levels when 2 clans merge, it removes the need for sucking in clans just to then kick them out.. there would have to be some sort of dual kicking out process. Eg. Leader of lower clan can request kicking out member from other merged clan but would have to be confirmef by othet leader. in other words, it would then take both leaders to finalize a member being kicked.
If levels average, not sum, meaning that the higher clan goes backwards, it would be better for the members of the lower clan to leave and join the higher clan.