For me, i do not bother with more mathematics. I have dreads with full supporting units.

and losing armada/fleet is very rare for me (no matter what defending units they have) most of the time what i lose is merc & pirates.

My army consist on following units

Plague Ship --> Juggs (White, Blue & black Sails), SOLS (White, Black Sails), Schooner (White & Black Sails)

HMS Invincible --> Brethern Frigates (Blue Sails Only)

Le Grande Cannon --> Bombraiders (Brethern, Veterarn & Normal), Lugger (White & Black Sails), Mitrailleuse

Captain Flint --> Buccaneers, Duellist , Marine

Reason is they are faster among their tier, together they form a invincible offense against any type of units.

But when raiding a bastion or a presidio and you know what is inside of it...the troops weakness count ..to make the attacker loses less.

yes that is why i mentioned couple of things which looks like you missed.

and losing armada/fleet is very rare for me (no matter what defending units they have)

Reason is they are faster among their tier, together they form a invincible offense against any type of units.

For me, i think the troops i am using are the best, just checked some stats and nearly they form equal offenses for all type of defense (with armada being 30% of total, and 30% of pirates, while fleet & merc stays @ 20%)

and than it depends what is against you, it is possible some BH's have targeted defense for Armada (without intel, every unit will fail), in that case you will lose the most of it.

to minimize your losses, we need a full intel on enemy defenses & than we can form our offense as per the need.

Here's a tip to help you. Look at the BH look for these following things:

How many members do they have? The more members the more likely they have a stronger defense

How many presidios do they have? If they have presidios that means their defense is spread. The more presidios means they had to spread their def its not centralized. However if taking on a BH with only one presidio look at the level of the bastion. If its level 5 then its likely they didn't defend it, don't waste your time hitting it. Look at the presidio but a BH in this category is going to be the same as a BH with no presidios or a bastion of a level greater than 5. They're defending with most likely all they got. 

When hitting bastions or presidios, you want to be diverse but if you happen to go with one unit type like jugs/sols then make sure you have the force to make a solid dent or take it down.

Since you've started about Dragon units, are they really worth it?

I mean they are cheap to train but the upkeep is high (8/4 rum per hour ships/mercs).

Since you've started about Dragon units, are they really worth it?

I mean they are cheap to train but the upkeep is high (8/4 rum per hour ships/mercs).

So far I've been getting them from prizes and exchanged them for Man O Wars and Submarines.