Interesting, and thanks for answering.
I did end up figuring out the implicit AND - essentially these are listed as object properties not within an array (OR syntax). In this sense, the REST syntax is slightly different than the GraphQL syntax.
My only issue now is using a query with multiple OR clauses. Currently, only a single OR clause can be used in a complex query using GraphQL. My ecommerce use case does require complex filtering such as:
Category A
AND
OR Brand A, Brand B
AND
OR Style A, Style B
In English - show me Sneakers made by Nike or Reebok in high top or mid top
Perhaps this example is part of the issues you mentioned.
I find Strapi very interesting and understand there are many improvements underway.
I will take a look at using REST