In terms of the player flagship, it seems like spamming Proximity Charge Launchers (PCL) is a very effective strategy. It has very high burst DPS, it takes out missiles and fighters (so it doubles as PD), and it has good anti-armor and anti-hull damage. It also inherits your momentum so you can launch it forward a lot farther than its range by using a maneuverability ability such as Burn Drive.
The epitome of this is the flagship Onslaught XIV, which is what I use as my endgame flagship. The large ballistics have Hephaestus on them for general anti-armor and anti-hull damage, while the rest of the slots are dedicated toward kinetics for anti-shield. (I'm also experimenting with the center large ballistic having Mjolnir instead for additional DPS and anti-armor, at the cost of flux.) I manually control the PCL's, using them to take out missiles that I don't want to absorb with my armor, and I'll manually toggle off the large ballistics weapon group for flux as necessary. If there's a particularly big target (Brilliant/Apex/Nova/Radiant), or a group of ships together, I'll burn drive in toward them, spamming PCL's as I go in. It clears out enemy ships
very quickly.
In terms of the overall fleet (i.e. under AI control), right now it seems like the best way to go is massive long-distance missile/projectile spam. This ensures that the enemy fleet doesn't get close enough to be a big threat, allowing your fleet to spend its flux on attacking rather than defending. Since high tech uses energy weapons, this usually means midline or low tech ships. The best example of this is using a bunch of Gryphons (Squalls and Harpoons linked together, with an HVD), the most overpowered ship for the AI in vanilla currently, but other ships like the Conquest, Executor, Onslaught, etc. can all work. The AI simply doesn't know how to handle mass missiles very well, so this disrupts the enemy fleet from becoming a coherent mass and lets your fleet pick them off.
Thus the most effective fleet I've found for general use is flagship Onslaught (player control) leading a bunch of Gryphons. It's the fastest at steamrolling through pretty much any enemy fleet up to and including multiple Ordos that I'm aware of. However, the fleet I prefer is flagship Onslaught with 3 Conquests and 2 Gryphons for more XP gain, since this only requires 5 officers instead of 8, increasing my XP bonus. I made an example video of the fleet in action
here.
The theme of player power this patch is endurance.
Not really, CapnHector was going after 5 Ordos and hence the fleets had to be built for endurance, but there's no particular reason to do that in normal play since once you get to 2-3 Ordos you're already maxing out the XP bonus. In fact you generally have to modify the game (to make your fleet look "bigger" and more imposing) to get more than 3 Ordos to attack you at once in the first place.
A decent fleet should be able to finish off double Ordos in around 5 minutes or less, with the best fleets coming in at around 4 minutes or less (Onslaught + Gryphon spam comes in at less than 3.5 minutes). It shouldn't take that long. Player fleet power is about maximizing your offensive power without dying, to chew through enemy fleets quickly and efficiently, and currently the best setup for that seems to be mass missile and long distance projectile spam.