With their new nagging un-skippable updates, the future isn’t looking bright for this product.
 - http://docker-sync.io/
Granted, you can still build and install the docker cli and use it to interface with the daemon running inside of a VM for free, but I doubt it'll be long until they close that loophole. My guess is they'll either move docker cli under the same licensing umbrella or simply make it too difficult for most users to build and run in a standalone fashion on MacOS.
However, I do wonder, if Docker Desktop performance is worse than running Docker on VM in multipass/VirtualBox/VMWare, even if there is no file sharing from host OS.
 - https://www.docker.com/blog/deep-dive-into-new-docker-deskto...
The biggest issue I've found with this kind of setup is that file change events from the host don't cascade to the virtual machine using VirtualBox's shared folders. NFS handles this better (still seconds delay based on cache values) but that is then a problem for Windows users.
It's been a few years since I switched to using Linux natively so my knowledge on Docker for Desktop Mac mount strategies may be out of date, but at one point docker introduced options such as :cached and :delegated which can have a considerable improvement to container file access speeds. Additionally, I've heard of people using mutagen and nfs for significant improvements, but I've never tried that setup. Here's a long discussion about it: https://github.com/docker/for-mac/issues/1592#issuecomment-6...
As you said (and others in comments) bidirectional syncing with docker-rsync, or using NFS, is one way to have files synchronising but it always ends up being a pain.
I did use cached and delegated but it's nowhere near close to the ideal solution: removing macOS of the equation. At least until Docker find a real fix for those performance issues, if anytime.