On the contrary, the IH is wonderfully balanced up to about Level/ECL 100 and playably balanced up to about Level/ECL 200. After that it becomes crazy, but thats what happens wen you mess with beyond infinite power.
Ahahahahahahah. You make funny joke. It good. I laugh. Level 100 is already good enough to gain Shapechange, which is better than any other Divine ability. Miles better. By level 100 you can turn into an Astral Hydra and get a breath weapon that puts every actual damage dealing [Breath] effect to shame, and for fewer DvAs with a shorter cooldown time. Divine Breath x2 gets you 30d3 every 1d4 rounds. Polymorph + Shapechange gets you 8x40d12 every 1d2 rounds. I wonder which one's better. And you get Panversal, which is a Transcendental ability, and a bunch of other abilities. Or you can turn into an Elder Quintessence Elemental, and at level 100, with a bunch of class features behind them will utterly annihilate everything even vaguely CR-appropriate. That the Elder Unelemental isn't even that good a form says a lot about how good Shapechange is. And Metamorph can be got at this level too, which makes everything even more insane.
Okay, so that's just one DvA, but then there's the portfolios, which are all over the place. Just try to claim that Entropy (with its 'vulnerability' that's actually advantageous in many cases, the best [Effect] ability, easily the best Quasi-Deity ability, because it affects created undead rather than just summons), isn't much better than most of the others, or that Healing doesn't suck. Its Demi-Deity ability doesn't even do anything unless you're playing with a limited number of pre-3.5 supplements, its weakness is horrendous (especially if you're using touch-range healing), and all of its abilities provide healing, which doesn't contribute to your effectiveness in battle, and is so easily obtained out of battle that the need for a healer seen at low levels disappears.
The Epic and Divine (and also the Cosmic, which is technically available sub level 100) Combat Expertise abilities make attack bonus granting abilities more effective at raising AC than anything that directly raises AC.
All the [Effact] abilities that target things other than HP are miles better than the others, as the resource they target scales linearly with level, while hitpoints scale with the square of level, except Thieving, which deals so little damage as to be useless (and is generally useless as actual wealth acquired with money is pointless when everyone gets scaling artefacts).
And those are just the most obvious things, and the ones that didn't use any non-core material or even touch on the balance of class features.
I think thats a bit harsh. Just because something in a seperate book when added to over 1000th-level characters in my book just happens to be exploitable is hardly cause for comments like "DM Makes Something Up" clause that happens whenever you do anything with the IH". Thats like saying because you can make Pun Pun with WotC books that they are completely broken.
The mighty WotC with its dozens of game designers and editors still had loopholes in non-epic play. So what chance a book with one designer that takes the game into Level 1000 and beyond...?
Oh, this is nothing like the kind of optimisation work that created Pun-Pun, the Hulking Hurler or the Wish and the Word. Those things require complex builds, multiple splatbooks (usually crossing edition and campaign setting boundaries in ways that were never intended) and generous interpretations of the rules to become broken. The IH is broken on its own. With just it, the Epic Bestiary, and the SRD. Usually just by taking single abilities. You can afford Nullification, Enlightened or Abrogate on an item at 72nd level (which is 'wonderfully balanced', you're keen to remind us), and once you've got it, nobody can do anything to stop you. In the case of the two cockblock abilities because they basically stop anyone from doing anything, and in the case of Enlightened, because it lets you bootstrap your way up to becoming a High Lord by casting progressively better Epic buffs to your Int until you can meet the DCs of the spells that grant divine templates.
But the real reason behind "DM Makes Something Up" being the default response is that so many abilities are poorly specified to the point where using them goes beyond Rule Zero and into the territory of There Were No Rules So We Had To Invent Some. What does the Morale penalty of Disheartening Dodge apply to? How is 'place of worship' defined in Theopea? What do you have to do to be considered 'hunting' a creature with Telelocation? What does Spell Shot actually do? What does Self Mastery actually let you do? Do the template-granting DvAs increase ECL? Does Moonstruck do so (it gives actual extra HD, after all), how do the Legendary [Creature] abilities interact with bonus HD from class features, dragon age categories, and non-animal creatures? Do High Handed and other Improved Unarmed Strike abilities only function with natural weapons, even though it doesn't say this? What's your effective druid level for Dragon Companion, and is the HD limit before or after bonus hit dice? What does "You cannot change the anyfeat while you have a previous use of the anyfeat in effect." actually mean? Does Sideways Stealing provide any mechanical benefit at all? Do the armour mastery feats affect anything other than armour check penalties (by RAW they don't)? And that's not even going into Portfolio abilities, which are often even more poorly specified and subtly different from other identically named abilities, or combinations of abilities, or Cosmic abilities and above. And this didn't require dozens of designers pulling full-time work like you claim, most of those things become obvious if you actually try to use them under any normal circumstances, because the ability, as written, does not actually provide the Dungeon Master with enough information to use it in a game.
