How has the AI improved over Entrenchment?

I don't remember if they changed that in the dozens of updates since Entrenchment, but that is something you can mod fairly easily.

Well, do you have Rebellion? Does the AI flee at the merest threat of engaging in a fair fight, or do they only engage when they have a virtually guaranteed victory?

Well, I find the opposite is true in my case... too often I see the AI just suicide their fleet into my far superior defensive position...

Starbases screw with the AI. I find playing against Hard AI I have no shortage of combat situations. I'm currently playing Grindstones against all Hard AI with a Normal AI ally (might as well just be me out there haha). I've Novalithed a few enemies into oblivion, destroyed a couple of titans, decimated vastly larger fleets (again, Starbases wreck AI). All with my Marza (starting cap) and one fleet research. I have the second smallest fleet (the only smaller fleet is the Normal AI who is my ally) and am holding out fine.

Based on my tendency to have smaller fleets I don't notice the AI running away from fights but they may if the tables were turned and I had a titan and 300 or so fleet points of ships to there 200 or so fleet points but my fleets are generally much smaller, but more effective, than the AI fleets. I'm like the Canadian Armed Forces of space empires, small but effective.

The AI isn't nearly such a wuss and can sometimes surprise you.

Well thats encouraging to hear! 

Occasionally it even shows cases of Artificial Brilliance.

If you don't want opponents that are "wusses" then why are you playing against the AI when you could log onto Ironclad Online and play against humans?

To second what Ryat says, the AI has changed considerably since Entrenchment.  In fact, it changed significantly just during the update process for Rebellion as well.  I like a long game and tend to play in the vast single-star environment, and the AI that I am fighting against definitely poses more of an active threat than it used to.  It can not only be quite aggressive, but very stubborn on defense as well. 

Having been playing space-based computer strategy games since the 1970's (that's not an exaggeration, either -- the first used to run on a Raytheon 1000, which is a computer so old you apparently can't even Google it; let's just say the 1000 referred to how many BITS of RAM it had), I am very well-acquainted with a large number of AI's.  And this is probably the best, i.e. least predictable, that I have ever encountered.

Because humans bring their own problems to the equation and some of us don't wish to deal with it.

otros humanos se desalientan al ver que se prohibió en algun momento jugar con la faccion "advent" y juntado con que saben otro lenguaje (español por ejemplo) que es dificil para juegar en equipo se desaniman de todo intento (google translated, espero que no se malinterprete lo que digo por problemas de idioma, por favor les pido que cuando vean que esta escrito en otro idioma tengan en cuenta que no se puede explicar en profundidad porque los traductores automaticos por ejemplo "google translated" no traduce todo, desde ya muchisimas gracias )

other humans are discouraged to see it banned at some point to play with the faction "advent" and coupled with who know another language (Spanish for instance) it's hard for you to play as a team are discouraged any attempt (google translated, hope you do not misunderstand what I say because of language problems, please ask them when they see that it is written in another language please note that you can not explain in depth because automatic translators such as "google translated" not translate everything from already thank you very much)

Are you saying that you don't want HuyMac to tell you all about the disease called "Ass Funnel" (in all caps, of course)?

AMONG OTHER THINGS!