I have to disagree with what paramecium187833 said about the Advent.
Advent is the weakest faction early game, because it has a lacklusture economy unlike the TEC and to an extent the Vasari. By the 12 minute mark of the starting game, a TEC faction will have created 50-60 frigates along with a capital ship. By comparison, if you're not focused on booming (upgrading economy) and just purely building ships, an you as the Advent faction will be lucky to have 20 tempest or frigates which is not enough to stop 60 TEC Javalins, corvettes or frigates steam rolling you as the Advent player. It's not even a contest, you simply don't have parity with matching a TEC with economy to build the same amount of ships at the same time within the first 20 minutes of the game. This is against the hardest AI difficulty level I'm playing at.
The only reason I'm able to survive an early rush is because I'm using the combination of Rapture capital ship with Domination ability to capture enemy frigates combined with the minor faction Pirates tier 1 'Pirate Boarding Crew' attached to the Rapture to capture additional frigates. I'm not building any frigate ships of my own and just focus on building a second capital ship 'Progenitor' by the 4 minute mark which I'm using as a shield healing boat. By the 12 minute mark, I'm barely able to survive an early rush with my 2 capital ships, and a dozen captured frigates with this strategy.
As for the Tempest missile ships, they are the weakest missile ship compared to the other faction missile ships. It has zero pierce damage, and its damage output is lower than the others. It's only saving grace is the missile redirection upgrade.
Iconus Guardians are cruisers which means you have to unlock the tier 2 and tier 3 to unlock both the ship and it's abilities and that is not cheap. For the cost you pay for, you'd want to expect that Iconus Guardians to be useful. The shields are strong, but it's hull is weak, so once its shields go down, it's very easy to destroy it. Secondly, if you are firing on multiple targets at the same time, Iconus Guardian shields will go down rapidly within seconds because it's absorbing damage for multiple nearby ships. Once it's shields go down, it stops absorbing 50% damage from nearby friendly ships and effectively becomes useless in combat. I don't think it's overpowered at all.
Same thing with the Illuminators, you have to unlock the hostility tiers to be able to unlock Illuminators and that is not cheap. And if I'm being honest, in over hundred hours of playing this game, not once have I used Illuminators at all. Simply because ever since they took out the Deceptive Illusion ability in sins 2, which was a damn useful ability I haven't really found a use for them. It cost too much to research and build illuminators early game, by late game their usefulness is situational and by use case scenario because they are too squishy without a bunch of iconus guardians protecting them.
Even if you think Advent tech is half price, you still have to remember that Advent still has the worst economy in the game. If you want them to have the same price as the other faction, then it would take more than 4 hours just to research everything without investing heavily into building a fleet. Sanctuary spire helps but it's not big a boost as you think. I'm 6 hours into a game with the test build version, and I'm only getting 60 credits/second and that is with all my 20 planets upgraded. The impossible TEC AI is floating over 2 million credits and is filthy rich. And that is because the Advent don't have trade ports unlike the TEC. In a war of attrition, if both factions had to continue to replenish their fleet building ships spending resources, Advent is going to run out of credits long before the TEC faction in a long game.
Shield burst is a useful trade off for TEC having ridiculous 15,000 to 45,000 crippled hull points (with their Titans and capital ships) which takes so much firepower to chew through. If I have to imagine the TEC having shield burst on top of that insane high crippled hull points and armor points, it take a 2 minutes with 2,000 bombers sustained fire just to bring down a titan. That would be ridiculous.
"Vasari don't perform well against Advent". Are we playing the same game? That's not right at all.
TEC performs well against Vasari
Advent performs well against TEC
Vasari performs well against Advent.
That's how the meta is. I have to kite the Vasari fleet to stay out of range of their 50% phase missiles with a fleet of halcyons if I don't want to lose a ship. And to say that they can "fully block" missiles is not true. If I go stand toe to toe in a slugfest, I'm going to lose 3 or 4 halcyon carriers to their 50% phase missiles, long before my carriers shields go down.
Anyway there's just so much wrong with your feedback that I had to chip my two cents here. There's some things you said are true but there's alot that makes no sense.