I don't know if that necessarily holds true anymore. The Advent titans can give newer players a much tougher time than say the Vasari ones, which need more skilled used of their abilities, and some of their stupid use of resources have been corrected. I wouldn't worry too much about which faction the AI is playing as, yours is far more important.

In the 1v1 SP games that I have played, I find that the Advent Rebels actually give me the most competition.  The AI seems to use the Eradica Titan very well.

Also, the Advent have the strongest defensive structures in the game after they get the research that give structures shields.  This effectively triples their durability.  It isn't a big deal against a human because a human player will just go around them, but the AI seems to always attack defensive structures.  And the Advent AI seems to like to build a good many defensive structures.  This gives them a substantial advantage defending in AI vs. AI battles.

With all that said, I would suspect that Advent AI would do at least as well as the other races in the scenario you described.

Basically phase missile research gives those units a chance to bypass shields and most importantly shield mitigation. Since structures by default have no shields or mitigation, to unshielded units phase missiles do nothing, it just gives a chance of treating a shielded target as unshielded. Phase missiles will have a bit easier time dealing with structure shields (and Advent in general with their shield focus), but its still a pretty big boost versus having no shields at all.

At the highest upgrade level, Phase Missiles have a 30% chance of bypassing shields.  So let's assume you have 10 Phase Missiles that do 10 points of damage each (For the sake of simplicity we will also assume that the target is under fire and its shield mitigation is all the way up to 57% and that the targets armor level is 0).  Without the Phase Missile upgrades, these missiles will do 43 points of damage to the targets shields (10 * 10 * (1 - 0.57)).

Now lets add in the Phase Missile upgrades.  Of the 10 missiles, 7 still hit the shields, but 3 get past them.  In this case 30.1 points of damage is applied to the shields (10 * 7 * (1 - 0.57)) and 30 points of damage is applied to the hull directly (10 * 3 * (1 - 0)).  This gives a total of 60.1 points of damage to the target and a damage increase of 39.8%.

The reason fully upgraded Phase Missiles are so dangerous to the Advent is because their ships have more shield points than hull points.  From the previous example, the damage to the hull was about equal to the damage to the shields.  Very often Advent ships will die with a good portion of their shields left.  When you factor in the shield mitigation increase that higher level capital ships get and the shield mitigation increases from culture, the effect is even more pronounced.

In my opinion, they are, although it is close.  Meteor Storm and Mass Disorientation are very good starbase abilities.  Add in the shielding on structures and you can really build a fortress.

Twin Fortresses is pretty good (I tend to use the second starbase for lots of fighters) as are the Gauss upgrades.  The other key defensive tech they have is Militia Armor which significantly increases the durability of all units (ships and structures) when fighting in a gravity well you own.

Which of them can "survive" longer until your fleet arrives, TEC or Advent? I see my TEC fortress being somewhat easily destroyed even with all the upgrades, etc. I mean, it's good to have 2 Starbases but I would rather have 1 that could survive at least 50% longer...

But I would also like to leave 2 slots, 1 for trade and 1 for Auxiliary Government... which would leave me with only 6 for weapons/armor/hangar. Would an Advent Starbase with that still survive longer than a TEC one with 8 upgrades on armor/weapons/hangar?