I have beaten the 6th gym a while ago, and I have just bred a competitively viable Gible that I have levelled up all the way to level 88 using the Audino trainer with his 3 level 80 Audinos plus the Lucky Egg in effect. But as the levels go higher, the exp yield lowers, and training is starting to get tedious. Is there a better way to gain levels “late game”?
No. Only a few Pokemon can be repeatedly encountered at very high levels, and even at level 120 (with Pokemon which adjust levels such as Rotom) it would have to have a very high base experience gain to beat Audinos. No Pokemon that gives 260 or more base can be encountered repeatedly at very high levels.
Edit: If you traded your Pokemon to someone would getmore experience per battle. I doubt anyone would do it for free though.
Insurgence has turbo speed with which you can increase the speed of the game, press M.