This matches what I’ve been seeing as well. Small teams can move surprisingly fast now, but the bottleneck usually shifts from engineering to distribution and positioning.

We’ve found that building the product got easier, but turning it into a sustainable business still required just as much manual effort around sales, onboarding, and retention.

You're moving the goalposts; building the product never equaled writing some code, it's always involved all of the efforts you reference. The expectation is that you optimized the code generation and shifted the bottleneck, but are overall more productive (i.e. the cycle is shorter). If you're not iterating faster then there's be no productivity gain.