I don't know in wich arena tier you are, but unless it's Platinum your opponents don't have their great hall fully upgraded. I'm in Gold I, my great hall total bonus is 53. The great hall is even more "long term goal" than any other stuff in the game.

Farm  more  gear      Im  in  G4  great  hall  is  lv  112    

G4  is  getting  difficult    i  havent  had  to  change  gear  for  about  6  months    Now  i  find  myself  trying  to  get  more  speed  gear    my  312  siphi  use to go  first  90%  now  she  goes  first  75%  

basically  me  being  in  g4  for  a  long  time  and  i  still  need  to  farm  better  gear with  speed    

Yep,same answers,farm more gear,upgrade more champions,eventually spend more money.I was in gold 4,now hardly can stay in gold 2  My great hall is at level 33 now,strugling for like 3-4 weeks to complete the Arbiter mission to upgrade a great hall bonus to level 9   The only thing that nobody understand is that after so much grinding,money spend,efforts to reach high arena tier,to can complete the Arbiter mission,upgrade great hall,and when finnaly seen a little hope,and joy that my efforts was not in wain,is just really frustrating to get trow back in arena,facing just unbeatable opponents,so my goals in this game was trow away to miles,and i can not have any hope that farming more,spending more will help,anyway can not find that enthusiasm what was at the beginning.  The irritation,the frustration is too high,and i can just blame myself how idiot i was to spend money in this game,where overnight everything you built can collapse.