What you say is true. There are currently 3 different ways to show the excerpt. The only want I can think of to adjust how much is shown is with CSS using the GD Post Meta for post_content . That will put in a gradient that can be adjusted with CSS on the height to adjust how many lines are shown.
Instead of that, you might consider using a custom field that has your excerpt, then hide it in some views.
In either case you will need CSS targeted at the specific GD Listings blocks you are using.
I will share your request with the developers but at this time there isn’t a plan to add that functionality back in. I hope you can understand that is because there are now several other ways to achieve the same outcome, methods that were not available in GDV1.