This is the key issue, loss of flavour and aroma. If it is there in the FV, pre-packaging, then your technique works, and I wouldn't get too wrapped up in changing hop types, using different bags etc.
The problem is in packaging and more importantly oxygen pickup. The first thing to suffer when oxidation occurs is hop aroma.
What is your bottling technique?
I have a simple beer siphon that you push into the bottle, fill to the top, pull up and the siphon holds the beer ready for the next bottle... I don't have a beer gun or use CO2 so only O2 it gets exposed to is to lift the lid on fermenter to put siphon in and when it pushes O2 out of the bottle...
Interesting on the O2 front. Friend has a grainfather setup and recently been getting the same problem and in reality getting no better results than myself which is basic BIAB.
I limit O2 exposure as much as possible and using my methods I can't see how I can improve that without investment in a beer gun for example...
I still think there is improvement in what I have to begin with before more investment. I believe if you can learn to brew better to begin with using simpler methods then the additions of more expensive equipment will improve rather than cover failings in my understanding and processes
My next step is to let the hops steep for 30 mins after flame out rather than cooling straight away. Hopefully that extracts more out of the last 15 min hop additions