I've seen the opposite...I play on Nation difficulty with 4-5 AI opponents, usually on larger maps so one can establish themselves.

Unfortunately the last few games I've played I restarted either because strategic resources were not bountiful at all or as in the last game, we're on turn 63 (Fast speed ~ 150 turns), I'm in Medieval Era, everyone else is in Classical still...yet the leader has twice my fame (3200 to 6860...second has 6450...third 4900).

I also have only met one AI and they declared war on me as soon as I built an outpost on their continent and I refused to 'give' it to them.

I built up an army of hoplites (like 8) over about 10 turns and finally tried to invade a little to push them back.

I've won most battles, but the AI continues to spawn groups of 4 units (2 emblematic, one archer, one scout) all over the place.  There's been at least 24 enemy units I've seen on the board the past 5 turns.

I would go broke and have no population if I even tried to build that many units.

Point is, for the way I play...and with updates made due to people apparently thinking the more normal levels were too easy...it has now made the game impossible for me to play and feel like I have a chance.

To make matters worse, I am always hampered by hostile independent people...who also seem to have much larger armies, especially for the Era.

It's almost to the point I no longer want to try playing anymore...and I've been playing since the first Open Dev

Well, I'm on the too easy bandwagon. I just played a game (huge, most elements randomized, endless, 10 players (all AI + me), Humankind difficulty) to test some personae and decided early to just let the game go its way: no war, no tryharding. I did not really paied attention to many things and let the game slip away, or so I thought when I realized I was almost one era behind everybody, safe Leonardo da Vinci (only persona not from G2G) and 2 eras behind some players (there was ~140 turns between the first player entering the last era and the end, ~80 turns between „the race is on“ and the endgame, the game lasted ~470 turns). Weirdly I was able nonetheless to build a luxury manufactory. 

I did a very peaceful run: Olmecs (weak!) into Mauryans, into Franks, transcending, Italians and one turn in the last era after transcending just because it was the last round, because @RedSirus decided to complete the tech tree, while being 3rd. I end up second with 21K, the 1st having 21,6K (having Workaholic and Engineer as traits...). I never got attacked (I had a pityful not up to date army), forgot many trades, didn't took the time to build my science early enough, as I thought the game would end. Truth is, if I'd reload around turn 350, I'd win, pushing it a bit harder.

So, I end up second but it feels too easy as I did not really pushed myself and would have won if so. I'm a decent player, but far from the best and could not hold my own in MP against the furious mind that populate some threads. I wonder where is the challenge for such players when they play solo. For those that find it too difficult, it is still possible to play a level below, but above Humankind, there's nothing.

EDIT: I forgot: first time that I do reach (well other players did it) the last level of pollution: I saw no change in my game... (the option was ON) Wonderful...