Any creature? I kind of doubt someone who's been exposed to Delver of Secrets would find a
Graceful Cat particularly threatening.
Even if we limit ourselves to the cream of the crop, creatures honestly haven't gotten much better since 5 years ago, which if you'll remember was around the time of Avacyn Restored's release. If they've already been exposed to Tarmogoyf, Delver, Griselbrand, etc. then what new creatures are going to shock them that much? Maybe True-Name Nemesis simply for the absurdity of its design, but that's really it.
If I recall correctly,
Treasure Cruise and
Dig Through Time got banned in Legacy, so that's what happened to them.
But those creatures aren't that great. Look at the cards: Felidar Guardian, Emrakul the Promised End, Smuggler's Copter, and Reflector Mage. Are those among the all-time great creatures in Legacy? No. Do they even really see play? Emrakul and Smuggler's Copter sees a small amount of fringe play, but the other two see zero. Even if we move to the lower power Modern, all four of those cards are fairly fringe.
So the idea that they're some kind of power creep past where we were 5 years ago is obviously pretty false. Take those creatures, then compare them to Delver of Secrets, Griselbrand, Snapcaster Mage, and Thalia Guardian of Thraben, which have all made a big splashy in Legacy and (except for Griselbrand) were highly prominent in Standard.
So, what's the problem with these creatures, if they're not really an improvement over what we had 5 years ago? The big problem with Standard is how awful they've made the
answers. Not just in terms of removal, but in terms of general answers. Consider the fact that
Grave Birthing is one of the best graveyard hate cards in the Standard where they decided to print Emrakul, the Promised End.
Do you think Emrakul would be as powerful if something like Scrabbling Claws were played? Do you think Smuggler's Copter or CopyCat would've been as powerful as they were if Pithing Needle were around? Reflector Mage (and also CopyCat) would've gotten a lot worse if
Torpor Orb or even
Hushwing Gryff was legal. But none of those cards are legal.
So the problem really isn't the creatures themselves, which as noted aren't substantially better than what we had 5 years ago. The problem is the general Standard environment. If you look at every previous Standard banning or restriction since the format's reception, almost all of them, at least at the time, were a big force in the larger formats (and possibly got banned there at all). Stoneforge Mystic, Jace, the Affinity cards, Skullclamp, Dream Halls, Lotus Petal, Tolarian Academy, Windfall... you look at those cards, and then you look at Reflector Mage and the contrast is obvious. Even cards banned/restricted in Standard that seem goofy nowadays (like Fork) were at least considered really good in larger formats
at the time (Fork also got restricted in Vintage). Not so with these 4 bans.
I know here I'm just saying what I've said repeatedly in other topics and other boards, but that's really what it comes down to. Standard isn't messed up because the creatures are overpowered (granted, CopyCat by itself is pretty innocuous, it's the combo that's the problem--but that combo, which took up something like 40% of the format in Standard, is an utter nonentity in Legacy and isn't seen much at all in Modern), it's because of the weakening of answers to the point those creatures have become an issue due to the general context, which is why cards that would be utterly laughable to ban anywhere else are considered so broken in Standard that they necessitate bans.