I think what the OP means by winning is keeping control of the gym, to your point exactly.

I am also at level 23 and can take out pretty much any gym. But right when I walk out of range, someone half my level using either a full six roster or type advantage or both will boot me out. When the game came out I could maybe stay in control of a gym for a day but now it has not exceeded half an hour so I no longer try.