Valuation to me doesn't mean much until the company is bringing in real money consistently.
Because soon or later you are going to run out of money and you will just wait for acquisition.
Also, I have never heard of Thumbtack since its debut (over six years)... that's just my opinion.
Time to re-read @paulg’s “The Submarine.”
Everyone from "startup banks", to payment-processors, to service marketplaces, to coworking spaces, are all running full-tilt toward this goal, and getting a company there first (and achieving a network effect from doing so) is what has the all the investors interested.
I mean, being a middleman, I understand... but most of the middleman networks start out as a thing, and largely stay that thing.
I'm not saying you're wrong... just trying to understand what you are saying.
The main method of achieving this goal, from the starting point of having any one "component" of such an offering, is merging with other companies that provide other components, or integrating others' components into your own as a "suite" or "dashboard", or selling a "concierge" service that recommends others' services, etc etc.