You guys should see brake lines that are really worn out and feel them expand in your hand...it makes it much more obvious what's going on 😄
All materials in nature respond to force, pressure or otherwise. Even when you're pressing your hand against a wall. It may be imperceptible or trivial, but they do. In the case of brake lines, expansion of the brake lines under pressure reduces the overall pressure. This will reduce the overall pressure going to the piston and we'll feel it as "sponginess" or similar words.
The ideal brake system has zero movement at the fluid boundaries except at the master cylinder and the piston. But that's impossible in the physical universe. So higher end brake systems will have higher degrees of stiffness at the boundaries, whether it's stiffer fluid lines, single piece vs. two piece calipers, etc.
Anyway, yes...SS braided lines do increase overall force to the brake system and reduce sponginess. Whether it's a trivial or significant amount is both a math answer and a subjective one. I'm pretty happy with the stock 6th gen lines at 18 years old, although admittedly I'm not pushing them very hard. But I've changed lines on bikes that desperately needed it. My truck could really use some SS lines, along with a couple other things.