I attached a pic of my highest level tame which is about to hit 197. Something on my end is different but the only things I changed when this started working for me are the experience cap and the level ramps. I can't find any other relevant settings but I've also attached my other config files in case anyone can find something I missed.
Edit: I just noticed an oddity. I have a tiger I managed to tame at level 179 that isn't gaining xp.
GameUserSettings.ini
ServerGrid.json