A site for freelancers needing extra manpower from skilled "sub-freelancers" isn't such a bad idea. It could be sustainable and profitable. I wouldn't discount this idea too quickly.

IMHHO ignore "eventually will have to move toward xyz" thoughts creeping in at this point. No path is a must follow. Maybe there are third or fourth directions it could turn toward.

Again, hard to give concrete advice with the limited info, but:

(I) The site is not ready or close to ready. Start with a newsletter or email list maybe? Can be weekly or ad hoc. Potential hook: "Are you a freelancer who would like to be notified by email ONLY when a fellow freelancer needs some extra help on a big project that pays $ and requires skills you have?"...Time needed, skills needed, pay involved and lead FL contact info will be listed. Sign up here!!! (you can have check boxes for skills during sign up - verify if you can).

Or

(II) Decide if you want to compete/join freelancer.com and upwork.com market. Why? How? What's different? How different? Are you sure you want to?...Networking with freelancers won't be your problem - they will come. Client side noise is a bigger problem (some people call/lump this with "CAC"). Displacing or joining market incumbents will be a pain; Need a =>product and money and luck and energy. Not impossible biz to get into but a slog.

Start a new HN thread when that project #(II) is actually beta ready and you have a 1-2 sentence why your site vs freelancer.com or whomever.

I vote for #(I). I bet there are freelancers who need help on big projects and are looking for quality, reliable second pairs of hands to sub-contract work to. Use that experience and email list to decide if you want to devote your life to #(II) as that option is a not a side gig type of endeavor. GL!