does erkenbrands ability count against days rising?

Yes, it does -- if Erkenbrand uses his ability during a defense, he has taken damage "while defending" that attack, and you can't use The Day's Rising.

If they had wanted otherwise, the card would likely say something like "After attached hero defends against an attack and takes no damage from the attack..."

why would they release a leadership card talking about defending attacks and probably thematically fitting with rohan with a rohan leadership hero whose ability involves him taking damage?

To limit the card's power.

but that just makes me not want to use it. is it still good with him? i mean wouldnt it be significantly better on beregond who can get much higher defense?

Beregond will probably get to use it more consistently. But it's still a great card on Erkie. There will likely be plenty of times when you don't need to cancel the shadow effect and don't take any damage! The advantage with Erkenbrand is simply that it's an in-sphere card.

this is kind of getting off topic slightly now but should i be taking lore for healing with erkenbrand?

Lore would fit in well with Erkenbrand, because his ability can only be used 3 times in a game if there is no healing present. But it's no necessity at all. I built a few decks with him and all work fine, despite there I'm no running lore all the time.

Erkenbrand - Theodred - Faramir

Erkenbrand - Beregond - Brand

Erkenbrand - Idraen - Frodo