First thing is in the waiting lobby for custom games some how set it up so oppossing teams cant see what the other demigods are playing.     As the game progresses it will be more widely known which demigods match up good again each other and people will just keep switching demi gods which will cause thier opponents to switch so on and so forth.  theres ways to prevent this ill leave that up to you.

    Second is give more and better options on the citadel upgrades.  Games progress in too linear a fashion when one team gets an early lead.   And its repitive and obvious which direction a game will head in early on as theres not much the weaker side can do to prevent it.   

  A couple things off the top of my head would be: make mob spawns strength levels based on the opposing teams demigods levels, also make the buffs to monster spawns be better and availble early.  This way if a team wants to commit early to monster spawns they arent just giving them game a way by handing out free xp(well maybe they are) but at least it will be a better risk vs reward.   

 On the citadel a better building defense upgrade should be availble but it also should be expensive.  This way if a team is losing early on it should have a good strategic option to invest in and fall back on.  instead of just sit back and slowly get hammered on until the inevitable comes. 

  Maybe something like an upgrade you buy that gives your demigod a bonus if you are on your side of the map(aka defense)