I get your point. If they say "now you have interiors don't ask about more gameplay in your ships", then they shouldn't implement it. But it's not an excuse to say that Frontier is known for abandon content. That shouldn't be the case in the first place.
I fully agree with you that interiors and inventing gameplay around them should've been the developer's priority. Enough interesting stuff happens inside a space ship. It shouldn't be hard to figure out.
However, as others in this thread have pointed out, Frontier isn't great at iterative software development or long-term project management in general. This means that shallow, sometimes barely functional, and most importantly, non-integrated features get released – with barely any interplay with other features. Then, when the feature isn't popular with users (surprise!), it's a financial flop. This causes upper management, directors and shareholders to lose faith in the product as a whole – causing them to force the team to abandon the features and to take a short-term 'get-rich-quick' approach, worsening the same issues over time, and giving us bolted-on FPS gameplay etc. Such is the vicious cycle of "miles wide, inches deep".
Like you, I see all the wonderful opportunities ED is missing. But I'm fine with all of the above because I still really enjoy Horizons. I worry however what will happen to Elite if Odyssey isn't a success (which I'm afraid it won't be, unless it was very cheap to make).