Oh I doubt it, unless you have that person with vision to interpret the results of the usability testing and turn them into a single cohesive design.

Good UX comes from someone that has deeply internalized the problems a piece of software is solving for users and the constraints on those users. Most startups do this without usability testing by doing things like sales or customer support. Anyway, IME usability testing is not the bottleneck to good UI.

I don't disagree with you that you need to have a singe cohesive design vision based on solving for users. But I think that certainly usability testing can lead to even better results and is mostly constrained by cost.

For sure. But without a cohesive vision throwing money at it can only make it worse if it does anything at all.