Yeah, the problem with that is it doesn't really matter. If it is OP for heroic then it is OP period in general. Making overpowered stuff only available at high level doesn't fix it. There can be certain types of exceptions to that but most static benefits really should balance at any level.
That's not true at all. Being surrounded by difficult terrain at Heroic levels will be an issue for every enemy you fight - at Epic levels, though, you have plenty of monsters who teleport or have other tricks up their sleeves. You have Epic Destiny powers or consumable items that completely change the landscape of a battle.
I think this is the very picture of something that would be balanced at Epic levels but is too strong when compared to Heroic familiars. Hopefully it will get fixed in the compiled release!