Hey, first of all, thanks for the detailed feedback, it helps us improve the game a lot!
Let's start with radiance. You were correct to identify that Advents are not about a single high DPS gun, but more about several guns with less DPS. Radiance falls in line with this, so we always should compare total DPS (which can be difficult at times, because of multiple multiplications involved).
In Rebellion, Radiance battleship was one of the strongest capital ships in the game. A level 10 Radiance would defeat any other capital ship in a 1v1. The subtle changes in Sins 2 means there's no shield mitigation in this game where the Radiance shined which had up to 75% damage mitigation which meant only 25% of damage was hitting the shields in Rebellion. The other area it outshined was Cleansing Brilliance ability to shoot a giant honking lazer beam that could do thousands of damage per second and it was also AOE so you can wipe out dozens of frigates.
Illuminators are your anti-capital unit. However it is worth noting, that their DPS is split between 3 guns, with 2 of those being broadside.
It's true that Illuminators are better against fleets with their broadsides, but what made them so good in Rebellion was that they could use Deceptive Illusion ability which was the ability to clone itself so if you had 400 illuminators, in combat you could have up to 800 illuminators with half of them being clones which was very useful for drawing enemy fire and allowing illuminators to fight in protracted large scale battles against fleets. Sins 2, they seemed to have taken away the illuminators Deceptive Illusion which was their one defining feature. Which I don't understand why they did that.
This is also why Destra Crusaders performed so well against a starbase, even though their default DPS does not seem that high. They have 1000 pierce, meaning that they deal "true" damage to starbase.
Destra Crusaders unique ability "Ruthlessness" also seemed to be missing in Sins 2 which is another defining feature of this ship. In rebellion it only did 1.5 dps tick damage to all ships in the area which isn't alot, and barely enough to overcome even passive shield regeneration but that isn't what made it good. Why Ruthlessness was useful was because it was effective against small craft such as hanger pets (fighters/bombers) and corvettes who have low hull points.
In terms of unity, conversion is very offensive. You can grab planets from your opponent, disrupting their supply lines, or pushing faster through their defences. Also the recall ability allows you to save your fleet. This is best used for a titan save. If you play with homeworld victory disabled you could even move your homeworld closer to the frontline, to keep healing your army, without the long route back to the front line.
Conversion in Sins 2 is heavily nerfed. There's no good way to put this. You can only grab planets from opponents if your culture overcomes that planet, and if your opponent is smart, isn't going to allow that to happen by spamming culture stations to counter your culture. Deliverance Engine is heavily nerfed, you can only use it within one star system, you can't shoot it to another star system which you could do in Rebellion. Worse yet, Advent's Unity ability 'Conversion' does not work at all if your opponent has all their planets covered with planetary shielding. So not only is Deliverance Engine useless but also Conversion. The only unity abilities that are useful is Scrying for intelligence and Recall as well as the one that makes your planet immune to bombardment. The rest are useless.
Finally Eradica is great against single targets, like titans, capitalships or even starbases. You should not use it's default weaponary though. That has more of a support role. Instead, you should focus a lot of PSI on your titan, and use it's damage ability. That way your titan will have about the same firepower Ragnarov does, but you'd also have the suppression aura, to make enemy fleet weaker.
That's incorrect. The Eradica Titan is the best against fleets. It's actually the strongest titan in the game both in Rebellion and Sins 2 which mercifully, they haven't nerfed. I think you were meaning that the Coronata Titan is great against single targets.
Eradica Titan has Chastic Burst which deals a large amount of AoE damage (over 1000 damage) to a large area every 20 seconds (17 seconds with cooldown artifact). You combine that with its Super Saiyan on steroids ability 'Unyielding Will', and you've got a Titan that can take on a fleet and win in a slugfest in any 1v1 titan battle.
I actually understand where 
aigor85 is coming from. Ever since the changes in Sins 2, Advent have become somewhat weaker and harder to play in the early, mid and late game. They are very vulnerable at early game, with weak economy, and nothing to stop early rushes from either TEC or Vasari. In Rebellion you could spam 5 beam platforms with Protection of the Unity upgrade and culture upgrade that boosts shield regeneration by 150% which could fight off against any early rushes. 5 beam platforms meant that each beam platform had over 1,700 shield hit points which is almost equivalent to capital ship strength. That feature seems to have been taken out of this game.The beam platforms used to take only 1 tactical slot so you could have up to 40-60 beam platforms on a planet, but now they take 2 tactical slots which means you can only field 20 beam platforms which isn't enough to stop any invasion force.
Even now, I still haven't figured out a meta that can stop early rushes. That being said, I've adapted somewhat to the changes and can fight mid to late game and win without losing a ship now. As per the original meta of Rebellion, late game Advent is the strongest faction in the game (late game that is), but the weakest early game without research or upgrades. But it's the early rushes that I can't figure out. Without beam platforms "Synergy", I just don't know how I can stop early rushes. TEC economy means that by the time I have 20 frigates, TEC faction will have up to 60 frigates in the same time. Sort of the same with the Vasari.
