The difficulty level is unchanged for any of the COAS-based mods, so it is still rather ridiculous at the high levels.
The AI of ships is mostly script-based. The only engine modifications are that when the script tells a ship to flee, they will usually take smarter paths away from threats in Maelstrom. COAS script AI is unchanged. GOF has some modifications where they will switch ammo a little smarter, but if they run out of ammo or powder, both COAS and GOF will continue to "fight" without ability to even fire. For ERAS, the ammo switching is a little smarter with the added feature that if a ship runs out, they will attempt to flee the battle.
Also for ERAS, there are a few quest points that were modified to make it a little less brutal at higher levels. One case is the fight in the house during Isabella, where a short delay was added before the enemies spawn, to give the player a chance to position better, since the enemies are so fast and powerful and they quickly surround you and dead...
Another one I know that was modified is the Esmerelda shore where there are something like 10 enemies and none of your fighters can spawn there; if you have fighters, they will spawn, and at the lower levels, if you have no fighter support, not as many enemies will spawn.
In short, not much has changed, and I tend to only play at difficulty 7 or below because the original was not very balanced. However going through the entire mod code to adjust all situations and quests is too large a task to address as a solo developer that also has a day job.