Introduce dragon riders so just like how you would get dragons from chest eggs u would get riders from random market recruitment and each rider has a specific dragon that they have synergy with there will be an additional boost to overall power of the dragon and rider rider can be used for any dragon not necessarily only that specific dragon, the rider themselves can either be just for stat boost or maybe they have some skill themselves? For example spear throwing, Archery, expert dragon handling etc , I feel like this is a great aspect that can be used alongside with dragons and continue through seasons maybe these riders like they could have a similar thing as dragons where they are teens and when they reach 6 stars they become adults , teens with less boost adults with more boost .
This can definitely make the game more interesting because aside from combat combination we don't have much to play around with since most of the thing is more or less fixed .
Hope this suggestions helps!