You should look at the post about patch issues since different people have brought this problem up already.
I added a screenshot on this page to illustrate the problem of not getting any bonuses whatsoever in the Arena while your opponents do, even in normal difficulty, and from the answers, I’m not the only one.
Thanks Riversong, I first went to the PVP tab and selected defenders.
Then I went to my teams and created a new team in which I filtered my troop choices by my highest level town which is Divinion Fields at level 8.
Then I made a team with as many similar troop types I could, not caring if the team is actually any good. That team has pretty decent bonuses because of it. Then set that team as my team to defend.
Sure enough, when I went to start a new arena, the team I choose has all those bonuses I earned in my defending team. Thanks again, and I hope my process helps others get the similar bonuses .