First a short run-down of how combat works:
1) Every ship will target an enemy and fire its weapons one by one. If it destroys its target, it will fire any unused weapons on its next target and so on. This means a big ship with many weapons may engage and destroy several ships at once.
2) Defenses now recharge per round rather than per attack. This means that one ship will have its defenses tested against every enemy in the opposing fleet. If it manages to survive the round, the defenses are recharged before the next firing cycle begins.
3) Unless you have the super-warrior ability, there is return-fire provided from defending ships that got destroyed. In DL, 'getting the charge' was very important because any ship you knocked out didn't get a chance to fire back. Now it can.
4) In case of a draw (both ships/fleets get destroyed), the side with the most starting hp wins.
How this affects conventional wisdom:
1) Combats get a lot bloodier. Whereas in DL a ships attack value was matched against the other's defense value this is now the fleet's attack value against one ships defense value. It doesn't take a genius to figure out that as logistic capabilities go up, so will casualties.
2) Defenses aren't so much used to keep a ship whole as to slow down the rate of destruction for your fleet. In DL I used defenses when I out-teched my opponent or when the general level of tech was low (low attack/defense versus hp ratio). In DA I use exclusively all-attack ships. Some use other rules but the bottom line is, defenses are optional, not necessary.
3) Logistics aren't necessarily a good thing. If you are facing very big fleets with a high attack power it may not be a good idea to send in a whole fleet of your own. Perhaps an example will make this clear:
- The enemy has 5 frigates (20 hp) with 70 attack and 0 defense each. These are typical ships the AI builds on Tough.
- You have 3 dreadnoughts (110 hp) with 300 attack and 0 defense.
Supposing for each that each scores maximum power you will see that both fleets would be wiped out.
Suppose you would send in your dreadnoughts one at a time. One ship would wipe out the opposing fleet with attack to spare. In the return fire, only that one ship would bite the dust instead of two.
Conclusions:
The changes in the combat system has led to players using the system in unintended ways. Defenses are optional and logistics can turn against you.
Obviously this is just my opinion and this wouldn't be a forum if there wouldn't be someone around who thinks otherwise.