Another way to keep people from hopping
Clash of Clans already has the right idea with the profile stars. Now all that they need to do is make it to where the longer you stay in a clan and donate troops the more stars you get towards or the better Clan Perks become.
Say if you are donating 100 - 200 troops every season you will get an extra 1% towards Donation refund. Donating 500 to 1,000 troops an additional 2% refund. If you have been in the clan for 1 year you will get 2 minutes less on troop request time and an additional 1% war loot extra storage and so on.
The strategy is in the game already to keep people in a clan. Just need to branch it out more.