Live API Creator exposes views as endpoints because there are times data governance policies requires DBAs to expose tables as Views to mask columns. They can be hidden under Security, if not required.
In terms of nested table resources, Live API Creator actually optimizes the calls. If you are returning customers and their orders, Live API Creator actually makes one single query to get the orders for all the customers, and sprinkles the orders back to the respective customers as it prepares the JSON response. E.g. select * from orders where custId in (c1, c2, ..., c20) assuming Page Size is 20. See logs for how the queries are formed and called.
If a virtual relationship is being used to link the parent and child tables, you want to link them through foreign keys or columns with indexes.
As for the last comment on:
"In addition filtering is handled very poorly when filtering by a sub resource where the primary resource doesn't filter as well" -- please provide a specific example so that we can provide further guidance.