Watch the lever arm move as you pull the lever. I have ripcords on one bike and std cables on the other and with both, the brake lever stops moving at the point where the brake caliper lever arm stops. Suggests the brake lever ‘flex’ I feel is the caliper mechanism (BB7s and TRPs) more than the the cables. My wheels would be locked way before then. Ripcords don’t eliminate all ‘sponge’ but they are a good outer. VFM though? Not so sure. Shimano full-outers with dremelled flat outers + ‘sealed’ cap ends, good routing and a lightly greased inner cable still feel great after 1000s of miles.
I hate really rigid brakes anyway, they feel wooden. Some flex is good for feel and modulation. Some road disc bikes do feel very spongy on the shop floor though, I suspect a bit of set-up attention (caliper alignment, cable end tidying etc) would remove a lot of it.