I like it. It seems like you should have enough strength six to take down most transports and bully problem units (deathstars) at a distance. The avatar's buffs mixed with your baiting strategy nullifies a lot of the banshees' normal problems.
Considering your avengers are going to be at the front of your formation, they probably wont' be surviving to hold objectives. With this in mind, why not toss them and your hawks & spiders into an aspect host together to provide them with stronger shooting? Alternatively, you could throw the banshees and either the avengers or the hawks into an aspect host and give them +1 WS. This makes the avengers better at tarpitting certain enemies that charge them (anything with WS 5). Which is handy when you're in a fearless bubble. Giving the hawks +1 WS is very useful when fighting most walkers with your haywire grenades. The main benefit, of course, is letting Banshees hit most targets on 3s in melee.
I'm afraid I don't care for your storm guardians. The "flexible" squad doesn't work terribly well outside of Zone Mortalis, I find. You'll either be shooting at vehicles and wishing you had a pair of fusion guns or else you'll be getting assaulted or shooting swarms and wishing you had a pair of flamers. More defenders or avengers would make for a more solid marching column, I think.
You might also consider finding points to give your hawks an exarch with a sunrifle. His exarch ability is handy for harassing your opponent's backfield, and his sunrifle can cripple the shooting power of things like devastators or artillery.
My biggest concern if I were playing your list would be your lack of reach. You have a solid amount of strength 6 shooting, but not enough to make many sit-and-shoot armies concerned. Imperial guard and Tau will both be able to pick you apart at a distance while you're unable to do significant damage in return against their high toughness riptides and high AV tanks. The Avatar's bubble means that you can take a pretty big beating, but I worry you might lose your teeth trying to bring your main punch to bare.
I see this list working great against close combat armies like orks, 'nids, and daemons, and struggling slightly against mech and shooty armies.
I like it though! It looks fun to face and different from the norm.