The same way you knew it'd be good without having seen the other cards, you don't form your opinion based on the other cards since you don't know them. With the current knowledge, it's garbage other than gimmicky priest deck which probably still wouldn't use it over stormwind chargers so you can actually kill someone in one turn with all your spells.
Egg also looks pretty bad, but assuming the Whelps count as dragons, it might actually fit in a BRM new type deck.
Rend looks nice enough but require a dragon deck, and the stats are pretty garbage. The fact it can remove legendaries like Tyrion, Antonidas or the 4attack dragons(assuming they become relevant again due to dragon decks) over BGH is kinda nice. Especially interesting for a class with no good removal like Druid.