Commerce Tree for Domination Victory

First post, long time lurker. For background I play immortal level and most of the time (but not always) win. Can survive deity as world power but haven't won yet. On to the question at hand.
In my experience the commerce tree proves vital for late game war (generally trying to stop an AI science/culture victory or on continents when a run away emerges before I have chance to meet them). The crazy gold bonuses and purchase discounts allow me to match ai unit spam, and more importantly buy tons of nukes for a continuos nuclear disruption of the enemy's heartland. Without this I am not in danger of being conquered but lack the capital for aggressive war against a 20+ city Ai.
Obvious disadvantage to commerce is later (or even no) rationalism, leading to a possible tech disadvantage. This is nicely overcome by playing Assyria, but that gets old.
In your opinion is the it worth marginalizing rationalism in this type of game, or is science just too important?

Though my experience is with multiplayer Civ5, what I know of Commerce would apply to singleplayer in this case. If you're going Commerce purely for gold purchasing units, you only need Mercantilism, and that's close enough to opener for you to not have to sacrifice points in Rationalism.
Mercantilism + Big Ben + Mobilization lets you purchase units at 40% of their original cost (Mercantilism and Big Ben are additive -40%, Mobilization is multiplicative 2/3 multiplier). +1 Trading Post gold and Wagon Trains don't give enough gold to ever make up for not picking up Secularism and Free Thought ASAP.

What he said holds for SP. If your war requires science (and is not a crossbow/chivalry conquest for example) then take secularism.

The Deity AI cannot win before T280 most times, and the human can achieve an artillery win before then most times WITHOUT any Rationalism on Pangaea.

Taking rationalism is only worth it if you turtle first early game to get to Artillery T150-160 and then sweep a pangaea ASAP. But taking early capitals with Archers/CB/XBs is preferable for snowballing, and making Rationalism even less important.

For continents, I'd say rationalism is more important because the other continent is likely to have a runaway who will have flight and maybe more by the time you get there.

[EDIT: Protectionism is broken. Thanks for reminding me, Philip Wylie]

What about Protectionism in Commerce, surely you want to unlock this asap if going for a DomV. Every DomV LP I've seen tries to unlock this to take (usually) high unhappiness into happiness. I'm a fledgling warmongerer myself and haven't been able to unlock Protectionism yet either because I've failed miserably or the whole thing ends with me winning.

Definitely something I forgot to mention in the original post; Protectionism is to me one of the best policies in the game for almost any victory type (though the rest of commerce is not always worth it to get there). I have also found Mercenary Army very useful at times when on the defensive or after capturing a small city (low resistance turns), nothing liking popping 5-7 Landschneckts in one move. In MP (against friends who may admittedly not be that good) the low purchase price and ability to move on turn purchased can really put a damper on Keshik/Camel Archer rushes. The Zulu make this unit especially powerful through the Ikanda promotions; other than not upgrading to riflemen Buffalo Landschneckts are nearly as good as an Impi. The extra defense against ranged attacks combined with pillage city/tile abilities, super low price, and bonus movement can create a high speed force of early medieval attackers that barely need help from siege or ranged units. Just 10-20 can often crush an unprepared civ, and if a few die it doesn't really matter since they cost so little and only upgrade to terrible Lancers even if they survive (Though I will say Lancers with no movement cost to pillage can wreck an opponent's land particularly quick).
Having done my duty in raving about a unit everyone seems to hate, I have one more thing in Commerce's favor: Secularism is without question among the best buffs in the game, but in an ultra-wide/puppet warmonger empire there are likely far fewer specialists. Also everyone will hate you playing this way so the policy that grants +50% science from research boosts is not terribly helpful. Finally, a large puppet empire can make the Commerce finisher (+1 gold from trading posts) quite the money maker.

Landschenkts are especially fun with Sweden+Commerce - buy, move, upgrade to Hakkeppelita. You can end up with 4-5 of these on a turn for something like 2000 gold. And you can do it on your frontlines if you're on another continent It's a lot of fun pushing out a powerful force that quickly.

The commerce social policy is great for happiness while rationalism is good for sciences. The protectionism social policy is great because it gives a happiness foundation that doubles your happiness from luxury resources that you already have. If you're good at making science and stealing technologies then commerce can be the social policy for you. If you're good at being social and making people happy and are starting out then don't try commerce and try rationalism instead because you need happiness to make rationalism work. Purchasing is also really cheap with commerce, if you get big ben and adopt one of their social policies then you will be able to purchase anything really cheap.

10000hours said:

Landschenkts are especially fun with Sweden+Commerce - buy, move, upgrade to Hakkeppelita.

Click to expand...

How are the Hakkeppelita any better than regular lancers?

Now, Poland I think could really make this work! Forget about Tradition+Liberty and instead go Tradition, full Commerce, full Rationalism. Mercenary Army now gets you the only decent Lancer UU, and free pillage on top of that!

Commerce and Rationalism both buff Trading Post, but most games you have to choose between the two. But not with Poland!

The Polish UA is actually slow to accumulate, so I think it is a mistake to try and use it for early trees -- when they are only civ that allows full Commerce plus full Rationalism without hardly compromising Ideology picks. TP spam for the win!