RE: Difference between custom api and standard api
Hi, For the first question, in fact, the page you use in the Standard API and the page you use in the Web Service are not the same page. So the fields are not the same.
Tables cannot be published directly in BC, this has to go through page. (In addition, when you access Web Service, it is not actually API access, but Odata or Soap.)
I believe you have selected a standard page in the Web Service.
For example:
Customers: page ID 22.

But in api, page id 5471

For the second question, I agree with Josh.
So if the fields do not meet your needs, you should consider creating a new page yourself, publishing to a Web Service, or creating a new API page.
Hope this will help.
Thanks.
ZHU