How to beat this?

Hello everyone! This is my first post here because I'm new in the game, been playing for 1 month, 2nd single player game, 3rd total. I'm currently kind of stuck on an emperor game (king felt too easy). Playing with Mongols, I have trouble beating Montezuma who has about 30 cities, 1200 manifactured goods and 1k crop yield on turn 300. Gpt is shadowed by Austria who has 1300 but we're in good relationships.

My situation: 6 cities, 4/6 coastal including the capitol.

I'm 2nd on Literacy, 4 techs behind Austria. I have research labs and factories(out of coal) in 3/6 cities, I picked order ideology and got 2 free tenets, further advanced into the factory science boost. Currently @ ~750 science per turn, ~100 cpt and about 50 fpt

Map is huge with 12 players. I feel it's the most entertaining option. I have friendship with almost everyone who hasnt yet fallen under Montezuma's control so it's basically 1v8 where 3 civs were eradicated and I'm the next one in his way. Ive got Assyria behind me and I have a bad feeling that he might backstab me.

My build order was scout -> monument ->granary (meanwhile enslaved a worker) -> archer to keep my worker safe (zulu was my neighbor and I heard hes quite aggressive)-> 2nd worker->shrine which didnt really help cus I I found a religion via great engineer+hagia sophia

Policy order: adopt tradition->adopt liberty->rush for free settler->finish liberty->open honor->2 policies there-> open rationalism+2 science per specialist then move to ideology.

I have an army of 6-7 infantries(growing) and some industrial era units to keep myself safe from all attacks but he keeps shooting everything that comes close to his cities with his bombers, apparently he has infinite oil when I have 4.

My question is: I focused myself on dominance as I previously did culture victory, should I still aim for it? I managed to capture 2 of his cities but couldnt really keep up with his production.

2nd question: is a xcom squad rush going to change anything? Im going for them now, to avoid his bombers.

Perhaps you will say that domination victory requires me to be more aggressive, way earlier in the game but Ive been fighting him since crossbowmen/keshik(knight) times but lately he really started to getting invincible

Thank you for reading all those paragraphs(if you have), otherwise still thank you for spending time in my thread.

Let the critics come.......

PS. Sorry I cant post ss's but I will try to, tomorrow eventually

Simply 2 ways,
First: try to keep him busy by bribing some one to declare war on him or bribing him to declare was on some one.

Second, Build range units. Using them you can defend agains big army because AI is not very smart.

For the immediate situation of him shooting everything up with his bombers and you having little oil you could start with 4 fighters on intercept as well as some anti-aircraft units shadowing your units. Make sure you build the aircraft in cities with xp giving buildings and try to get extra intercepts and you will soon be shooting down his bombers.

Also what is your gold situation like? Do any city states have oil? You could also buy from other civs so you can get more fighters and then some bombers if you want to go on the offensive.

What is monty's science like compared to yours? e.g. can you rush to something like aluminium or nukes and use your tech advantage to crush him.

Does he actually have fighters? Leads in with which expansion are you playing as BNW requires you to own all the capitals not just be the last owner of your own capital and also has spies so you can see where his aircraft are actually stationed. If he has no fighters you could simply build bombers, put a spy in his bomber city for line of sight, bomb it to zero health and rush in a fast unit which can cover 4 or 5 tiles to take it and wipe out his bomber force.

As your friends with everyone else and monty has been warmongering can you pay other civs to DoW him and make him focus in multiple directions as well as in the case of assyria give them another target to focus on than you?

As your playing huge i'm assuming your using marathon speed? which means you could still do domination but it your doing well in other areas it might be easier to hold out and win by other means especially if you chose a faster speed. A few well trained fighters, some AA and artillery will wipe out most offensives into your territory.
I would stop building infantry and concentrate more on ranged as these are much more effective combat units. Infantry/melee units are generally just meat shield/blocking forces to protect your ranged units from direct attack.

You seem to have spread yourself out very thinly in regard to social policies. Honour is relatively pointless as a tree these days. For a huge map i would have skipped honour and tradition and you could have spend them more effectively in maybe patronage while waiting for rationalism to open, in fact if you take patronage down to science from city states you can often skip rationalism if you can ally with a lot of city states.

As the mongols you should have crushed him with keshiks, move in, fire move out but it is a bit late for this now he has aircraft.

As you have mainly coastal cities, does monty have coastal cities? You can for example make a couple of ranged ships and start sniping his coastal cities using spies to see if he has bombers nearby. You can then burn his coastal cities or just let him take them back as that will have ruined them to a quarter of their size and destroyed most buildings. If you can do this to a few cities it will start to put a significant dent in his empire.
If you are happy to let him just recapture you probably want to make some cheap expendable units to actually capture the cities as you may not have time to withdraw them before he can recapture it so they will be destroyed.