The Harlies are fine. There's nothing in the slightest that's wrong with the fluff in taking a squad of them. They do tend to lend a helping hand once in a while.
Just to say briefly that unless you are playing a Craftworld with specific ties to the Harlequins, the chances that even if a single unit will turn up are very remote, unless you end up fighting Chaos, which is why I made the point about background.
They're also one of the best footslogging counter-charging Eldar units in the game! They get a large amount of attacks and can cause rending on top of that.
Their performance is actually not that much better than that of Striking Scorpions or Howling Banshees, except against a narrow selection of high toughness units, especially given that rending has been (mercifully in my view) toned down, so I think your analysis is rather fourth edition based. In addition, reprisals make a very nasty mess of them if you are not careful.
Editing: The above sounds argumentative- I don't want to come across as such, so please don't take it as such, this is just my own opinion, and other players are certainly entitled to disagree with me.
I didn't think you were being argumentative, so no worries on that score
To the revised list then:
It's much more cohesive, but there are a few areas which could be improved in my view.
Spirit Stones on all of the Wave Serpents is essential in my opinion. You cannot afford for your attack to be fragmented by crew stunned results, since it lets your opponent pick of your units piecemeal, and the Eldar will enjoy that one bit in my experience.
Two more Howling Banshees would be helpful if you could find the points, as you really do need the maximum size of squad here in my experience, due to their fragility.
I strongly recommend keeping the Fire Dragons in the Wave Serpent, since it is more resistant to melta fire than the Falcon.
If you really want to take the Falcon, I suggest replacing one Dire Avenger squad with Storm Guardians with two Flamers and a Warlock with Destructor, and then mounting five Dire Avengers (no Exarch) in the Falcon, and using it as a mobile scoring unit (the DAVU). If you do decide to opt for this plan, the Falcon will need Holofields in my view.
If this idea does not appeal to you, I suggest dropping the Falcon.
Swooping Hawks are very brittle and hard to use effectively. This, combined with the fact that if they arrive early, they will be very exposed, given that everything else is mounted in a transport, means that I feel you would be better off dropping them.
The Vyper is a horrible piece of equipment when equipped with a one shot weapon, since it costs too many points and misses too regularly, so I suggest dropping it.
If you want some heavy support in this list, then I recommend two Fire Prisms or outflanking War Walkers, since they can really help to thin out opposing infantry, and if you take Brightlances on the Wave Serpents transporting the scoring units, then you will be able to use them as additional sources for anti-tank.
I don't recommend the Jetbike route in this particular list, unless you can take two units, as they are rather a soft target when deployed alongside all those Wave Serpents.
You could think about taking the Autarch as your second HQ if you want to employ the reserves strategy, but if that doesn't appeal, then he isn't required in my opinion.
Overall, this list is definitely an improvement, but I think it still needs to be toughened up, and to have more effective supporting units.
I hope that helps.