As a preamble, I'd like to point out that nothing in any book suggests that you can't create your own non-epic spells. The only difference in epic play is that the ELH goes out of its way to encourage custom spell creation.
To be blunt, the ELH is rubbish and the Epic Spellcasting is the toxic waste of the landfill. Among epic players it is a commonly known fact that epic spellcasting's only useful purpose is to create stupidly long lasting buff spells and one or two other niche spell types. Any epic spell that deals damage is a waste of gold and XP because such spells are much easier to use as meta'd non epic spells.
Yeah, epic monsters are just not very well thought out. Any epic DM should really be tailoring his monsters to his PCs' abilities.
Well to be fair high level AC isn't supposed to stop anything, it's only supposed to prevent massive Power Attack usage. But again, epic monsters and epic play in general is poorly thought out.
I have come up with my own epic rules based on my experience with epic play; to play in epic under standard rules you basically have to be a power gamer, which I don't like. If you're interested I can provide you and your DM with them.