big old hole in no-code marketplaces

Did you have a look at Tabbli? They say it's easier than Bubble.
I do agree with you, the learning curve for Bubble is steep but you could maybe start with a template and go from there? Zeroqode has over 100 templates for just about anything.

actually I think WordPress really meet your requirement, it's lower cost and easier to start.

The reasons are not technical that Marketplaces cant be built. The reason is that there are so many reasons for Marketplaces its hard to define a platform with all variations and enough demand to stand on its own. The way how most platforms have embraced this is by creating templates on top of them to support marketplaces.

Webflow, Bubble and Tablii all have templates that enable you to build marketplaces utilizing the underlying CMS of the platform. The only one with a true marketplace solution is ShareTribe.

But sometimes if your Marketplace is simple enough it's easier to hack a native solution and reach your required end state faster than customizing and integrating off the shelf solutions.

I am happy to chat more to see if there are specific functions missing using the templates available as I recently developed a two Marketplace and found the most basic features available.

My initial reaction is that marketplace software is complex - and there are solutions for turnkey marketplaces, build-your-own, and in between. You seem to be hoping for turnkey marketplace software at entry-level pricing? I think that's where there's probably a disconnect, in that like some others have said it's probably not a great business.

It might help if you shared why you want this - what business will run it.

What was wrong with Sharetribe? That's pretty much what you've described but you said it takes too long to build?

Others:
https://www.shuup.com/
https://marketplacer.com/
https://mymarketplacebuilder.com/
https://multimerch.com/

Wix and Squarespace aren't great examples, in that they've both raised hundreds of millions of dollars and it took both years to add any payments or commerce functionality. Squarespace just bought a 50 person company instead of building their own scheduling/appointments software. And both platforms provide incredibly basic software - essentially static websites with very little by way of user accounts or interactive functionality.

If you want customization, flexibility, then obviously there will be a high learning curve for platforms like bubble and sharetribe flex.

I'm not sure how there'd be an out-of-the-box solution that is both easy to use AND offers great customization. It's one or the other usually.

You are looking for serious integrations, none of which would be easy to implement on any platform out of the box.

Bubble is hard, yes, but that's because it allows you to do almost anything. Wouldn't you rather have the ability to be able to customize heavily over being locked into a certain path? Just my opinion!