You can take a look at below link for crud operations via Data API, I have shared additional resources in my previous reply that can also help you with the setup and integration.
I’ve replied to the post.
The threads you shared are nearly a year old and as we are constantly improving the services, recently we have not seen any such API slowness issues.
In case you face any challenges, while working on this you can reach out to us on this community forums or in case you need in-depth technical help/architectural suggestions, you can reach out to us at Contact Us | MongoDB .