But saying "just Force Hammer it" is analogous to MtG arguments about powerful creatures that end in "Dies to removal."
Good decks either run more (and more efficient) creatures than the removal to swamp it, or creatures that are immune in some aspect. But yes, in isolation dies to removal is only part of the story.
In MW though the number of conjurations are you need to kill are more limited. Most books have Force Hammer/Hurl Boulder or a a way to kill it with a could of cheap creature attacks (Acid Ball, lots of piercing, etc). I think what Puddnhead is alluding to is that it's a threat that they will likely already have answers to.
That's not to say don't use, just don't rely on it...
Just because Surging Wave exists doesn't mean Battle Forge is a bad card.
It would if Surging Wave broke even or thereabouts. Battleforge is a good card because you are up actions and mana if they kill it, and lots of actions and mana if they don;t...
There are ways to protect it if need be, and any card that demands an answer is a strong card by definition. Infernia will definitely mess with a lot of popular (and niche) strategies, demanding answers or else, which might give you time or bring about a big momentum shift while your opponent drops everything to deal with it.
Yes, it may do. Here I'd be better with more Dispels mostly (I really wish it had got Bloodthirsty and Charge), but it definitely has uses.
I don't see my Arraxian Warlock (relies on +Melee far too much) or Adramelech Warlock (races incoming damage) using it, but I think it will go into one of my Necromancers, and be considered for the other. I don't have many books that would pay 4sbp for it though, but in some metas you may. Definitely an interesting card.