Yeah I play on Monarch Difficulty, Standard Size, Snail Speed and C2C Perfect World Map and I still get my butt kicked for much of the time. I would say I am smack dab in the middle with one half weaker than me and the other half stronger than me. Personally I think that is a good thing seems to be balanced in that aspect of the game. Its not fun to be at the bottom and it can get boring at the top.
I also (playing as emperor start with flex difficulty) have trouble keeping up with the AI at first. It may be map dependent (I am playing on giant map, ROM archipelego) or perhaps game speed (snail here). I was literally 20 techs behind the leaders when I first met someone from a different landmass (had 2 weak AIs on my starting landmass). Are you finding you streak ahead BEFORE bronze working/monarchy or only after? I suspect it's the city limits associated with civics (which are new in V15) that might be causing your AI issues.