There is old phrase "if it looks like an duck and quacks like a duck then it is a duck". But no-one's back crossed ducks yet. So perhaps we need "if it looks like an aurochs and moos like a aurochs then it is a back-bred bovine that looks and sounds like an aurochs".
I suppose there’s some sense in which they’re ecologically equivalent. Like if we backbred mammoths and they started acting as seed dispersers for Osage orange trees!
The way I understand it is that they are trying to breed back down lines. I thought that this was a discredited theory e.g. you cannot get a wolf from dogs (although that may be because dogs did not descend from wolves). You can get a dog that looks like a wolf but you cannot get a wolf (although you could get a pretty wolfish dog like a Husky). They'll probably get the same result with the Heck cattle but I am willing to bet nearly any amount that they will not breed the same temperament into their aurochs. It would be just too dangerous. From all accounts they were hell on wheels and noted for their evil tempers.
The question is what’s a wolf? If you can’t define it independent of its particular history, then you’re right – you’ve defined away the opportunity to make wolves out of anything else, even the descendants of former wolves.
If a wolf is defined in terms of its interactions with other things – other species, ecology, whatever – then if you have plugs for the right sockets, you’ve got a wolf. It’s fair to ask whether this simulacrum of a wolf is really worth making. We could, while we’re at it, make something better than a wolf, or an aurochs.
In the latter case, I assume better would mean tastier and less likely to gore random hikers!