In my professional experience, the only spec you get is a wishlist, never quantified, always vague. Half the work is figuring out what the customer wants.
The only metric that anyone cares about is speed. You need to go fast, but to where? There is no consensus.
That’s basically the only important context. If you can’t deliver that, it doesn’t matter how well thought through, extensible, or scalable it is.
The PoC becomes a pilot becomes production becomes an exit becomes someone else’s problem. That’s the SLDC that has gotten us to a place with endless amounts of terrible software everywhere you look.
Though, I’m optimistic that at some point, the software industry will be so saturated, all the products have all the features, and the only place left to differentiate or disrupt will be quality.
And a substantial portion of the rest is telling them why they might be better off asking for something a little different.
If that's not for you, you need at least a requirement engineer between you and the customer. That's also okay.
From my experience, getting things done quick is almost never relevant. Getting things done “cheap” is.
So it's a conflict of names, a matter of proper identification.