Alternative ways to programmatic read contents of External List with filtered view

In order to export the displayed contents of a BCS External List to Excel (see previous post), I first have to programmatically retrieve the contents in custom code. The External List has a filter applied to it's Finder method, set via the default SPView:

My first thought was therefore that below code should retrieve the same filtered external data as when rendering the BCS External List on a SharePoint page:

However, GetItems returns an empty collection. Upon debugging the called GetNotifications webservice method, I discovered that the filter-param always has value ‘null’. To me unclear why, since it has been set in the DefaultView.

Via internet search I ended up with an approach to retrieve the contents directly by invoking the BCS API:

However, although this approach works; it left me rather dissatisfied. Conceptually I want to export the contents of the same (External) List that I already have provisioned on a SharePoint page; so why should I have to dive under the BCS hood to get the same contents? Also, this code is very much aware / coupled to BCS API, while the 'Export SPList to Excel' functionality on itself is general. Thus, with some ample time available, I decided to analyze the way in which the standard XsltViewWebPart is issuing the external data retrieval – using JetBrains DotPeek reflector tool (as .NET Reflector is no longer free of licensee charge). It appears that this is done slightly different as my original attempt:

Not only is the code LOC of this far less, but also this code is general; applicable for both regular SharePoint lists as BCS External Lists.