Magento is B2B marketplace solution that targets SMBs and Enterprises. And it has no competitors in this niche.
I think Magento is probably not the best idea for a startup. This technology is really powerful and provides a rich feature set and customization abilities. But such a mechanism requires resources and professional skills that may be too costly while starting a business.
Though, if you have sufficient start-up capital or funding, Magento would become a great booster for your eCommerce business.
Take into account that it's pretty labor-intensive and time-consuming, because, as I mentioned, it requires a high level of tech expertise. Experienced Magento developers can consult you on many issues (just as good as solving them), from FAQs to backend architecture and Magento PWA benefits.
In my experience, business owners are ready to invest in high-cost Magenta support and hire Magento developers in 90% of cases. The reason is simple: the outcome is worth it.