The more i think about it, the more i think youre probably right and it will be an okay card, and probably slide right in where Transgress left.
I do think the legendary clause is going to be a big deal though, and will cause it to see noticeably less play than it would otherwise. Though we've only seen 2 gods so far, the Theros gods were sone of the most played cards in the set, and if these are the same, not being able to take them will hurt the card alot
There was another reason why I mentioned this being a thing. I had forgotten until now. I noticed that this set put a lot of emphasis on embalm, and recurssion from the graveyard. I remembered that your poll about Standard, and cards that they could introduce to 'fix' it.
Tormod's Crypt, being one of them, then I realised, I theorised that this set would put a solution to embalm, and like
Tormod's Crypt the have introduced this card:
I am sure you will see others, I think that
exile effects, therefore (
Transgress the Mind) won't be important, which will mean that
Open Heart has more of an impact. I do agree, Legendary is a problem for it, but from what I have seen of these 'god' cards they are not nearly as potent as the Theros gods.