Yet another boring "godlike is ez, i am amazing" post.
And your response was yet another 'if it's too easy, then it's your fault for playing it wrong' answer I'd kind of hoped we'd moved beyond this whenever someone points out balance problems and reached a stage where we can discuss the problems highlighted instead. For example, the answer to the Thalan tech tree being absurdly OP is not 'don't use the Thalan tech tree then', it is 'How should Thalans be nerfed or others buffed'.
The biggest issues for higher difficulties remain the AI scripts, which are difficulty-agnostic and so the AI doesn't take advantage of its bonuses efficiently; the lack of scripts for the mid and late game also mean that it gets much weaker very rapidly after around turn 100 or so. Froggy has already said, repeatedly, that he is not very keen on the data-driven AI for this, and he's basically right - as long as it's so heavily script-dependent for running its economy, it's going to get worse later on as the game develops, because the scripts cannot account for the massive number of possible changes in the game. It's actually become pretty good at marshaling forces and building up fleets now, but it's trying to manage it's economy without any real reference to the conditions in the game.
Governors are basically build lists which are a guess at the best possible order, which is highly situational beyond beginner play. Even though they've improved enormously with 1.4, they've gone from being completely incompetent to being merely reasonably competent. Until the AI can go 'hey look, I have this huge approval bonus from my difficulty level, maybe I don't need to build any approval buildings', this remains an area where higher difficulty doesn't help the AI very much. This gets worse the more planets each side has, since the human can and will look at the planet's needs and respond to them.
The strategic AI scripts are likewise just guesses at what the AI ought to be doing 200-300 turns into a game, often for periods of 100+ turns - with no changes to economic settings, build choices, tech preference etc while a given script is running. Many AIs get crippled by sitting at war for hundreds of turns, using the War AI script which means they stop expanding and researching effectively. DoWing every AI you meet, the moment you meet them can pretty much win you the game by throwing them permanently into the wrong script and causing them to miss out on a vital period for expansion, or to miss out on a set of tech weights they need to pick up good techs - resulting in them developing ships they can't afford to build.
The AI since 1.4 has been 'good enough' - we no longer get first-time players complaining that they've walked all over the AI on the highest difficulties, and it'll provide a reasonable challenge to the average player, on his 4-player medium map playing on Easy as the Terrans. Once some of the more glaring balance issues are settled (SB stacking, ship prices, movement, diplomacy), the scripts can be optimized much more aggressively... but really, there's big chunks of the AI which would be better off taken out of the scripts completely, even if it means modders can't play around with them anymore.