BGH literally makes a 6 attack minion better than the same minion at 7 attack, it very much limits design space because everything with 7+ attack has to have a massive effect or be severely undercosted in order to be close to playable and BGH is a big factor in that. Sure, there's other hard removal but BGH is neutral and also an insane tempo swing, if you spend 7 mana on a big minion (let's say, Illidan, he's always a fun example, and I seriously tried to make him work for quite a while) and it gets hit by BGH before it can do anything you're so far behind because it not only got killed for 3 mana but they also get a 4/2 out of it as well.
Shredder and Boom I think limit design space simply by setting the benchmark for their mana costs far too high, as when considering a 4 or 7 drop the first thought is simply "Why don't I just play Shredder/Boom instead?". Maybe limiting design space is the wrong way to express it, but those cards crowd out far too many (existing or future) cards at their mana cost simply by existing.
I personally think Thaurissan is probably fine right now, but will inevitably create some other insane deck(s). He alters how future cards have to be designed because if a new card will cost X you can't just consider what (10-X) mana of cards can combo with it, but what combos are possible if it, and every other card, costs 1 less mana, because there's literally no way (Snipe+spell power doesn't count
) to stop his effect triggering at least once. He's going to enable some stupidly powerful deck again eventually (I think he was the big problem with patron actually, as he enabled all the insane 1-turn combos, without him the deck would need at least one turn of setup that could be played around). You'd need a design team that's way, way better than what the Blizzard guys have shown themselves to be so far in order to avoid that.