So does that make them the worst eco race, or is that still vasari because of trade at level 4?
In my opinion yes. While the Advent do have an advantage in getting trade and culture up, the advantage isn't that big. If you're in a position where its a good idea to spend a lot of money getting trade up, you ought to be in a position where you think you're militarily secure enough to protect it, and that probably means you have a sufficient number of planets to afford an extra lab.
Another way of looking at it is that the Vasari have many more reasons to invest in civic labs than the Advent does. Before Rebellion, the only good Advent civic techs that didn't unlock anything was the tactical slots bonus at tier 4 and allure of the unity at tier 8 (though even this is probably not worth the effort). The Vasari get phase stabalizers and the ability to see all ships jumping in the entire system. Now global unity, Wail of the Sacraficed and Return of the Fallen/Reserection have kind of change this. But at the same time Vasari players have their key subfaction techs in tier 8 civics with Striped to the Core and Starbase Mobilization.
In short, for the labs the Vasari get many more useful toys out of the civic tree than the Advent do, so if I'm not in an Eco slot and I don't think I need to rush wail as AR, I'd be really tempted to just get the three civic labs for trade and then focus on military, since here the Advent techs are much better.
Does either have a fundamental flaw that makes them hard to play.... like Illums needing to be micro'd to the middle for side beam damage thus getting thrashed by titan AOE (completely made up hypothetical scenario)
Advent fleets definitely require more micro to get the most out of their synergies (or to maximize Illum output). However, the major titans with AoEs (Ragnarov, Eradica, Vasari after they level up) will make any frigates except Corvettes and Carriers obsolete, so its not a huge deal in that regard. However in my opinion it's worth it. Sins is regarded as much less micro intensive than SCII, so if you're used to that I doubt the timing and upkeep of using Guardians with repulse and keeping your caps close enough to buff each other will be too hard for you.
Vasari abilities tend to be powerful but can be more complicated than the TEC, but they aren't as dependent on synergies. If you want to get deep with the tactics the overseers capacity to fully heal a target near instantly in sufficient numbers or the subverters AoE frigate disable ability offer a lot of potential, but I personally have not seen them used in Rebellion MP games very much. Unlike the Advent, Vasari capitalships work pretty well independently and don't synergize (Skinatra's repair cloud being the main exception, but even this cap can hold its own 1v1 with scramble bombers), so you don't have the incentive to diversify your fleet as you do with Advent (though they have 3 top notch capitalships and only one totally bad one, so you can if you want to).
I'm trying to feel out the overall "philosophies" of advent or vasari and then I'll pick a faction from there.
In a nutshell
Advent - Synergies, Synergies, Synergies. Good military techs as well and offensively very cost efficient.
Vasari - Mediocre stats, but very awesome unique "toys" (phase stabalizers, phase missiles, jumping starbases etc) and abilities.
