A couple of things, firstly of course your strategy can be "wrong" on the default setting. Default is not best. It is simply default. Work on strategy and you can improve. Work out where you are going wrong by watching games, do you pass enough, do you kick too much or too little, are you giving away penalties, are you winning line outs. All these things and then make changes to your strategy accordingly.
But also, team average rating can be misleading. It is an average of the entire squad, not the first team on the field. If you have a squad of 23 players all of 20 (I'm simplifying here) then your average will be 20. But if you have a squad of 46, half of whom are level 20 but the other half are level 10 then your team average will be 15 but the fielded team can all be 20. If I see an individual player is beating my team then I check what level he is, it's not unusual to find a player of level 30 playing amongst a whole load of low level players, and that one player can be damaging.
I went through a patch where I seemed to be loosing to everyone. I had made too many big changes to my strategy. I now have a primary strategy and a test strategy. I make changes to the test strategy and if they seem to work then put them in my primary strategy. I'm doing better - although getting my behind kicked in the league championship, I have got through to the final of a tournament at last.