I don't understand very well all you said here...
If you play with the Beta version, the difficulty of your opponent is always in medium whatever you chose when creating your new game.
If you have 25% everywhere, it's sure it'll be very hard to beat a player with 75% everywhere.
You have to play in low rank tournaments to amass training points, and train yourself till you get good skills.
If you want general tips to beat the Easy & Medium, have a look there :
To return serves of strong servers, you should go a bit more far from the base lines, use the preview setting to see where the ball will land, and do some very little left-right movements, to start to run faster.