I like banshees. They are a decent unit, and will hit many of the units in his list pretty hard. The preferred war gear for the exarch is the executioner, the extra boost in strength is much needed, and since you can only assault out of a wave serpent that
hasn't moved you'll be fleeting most of the time to get into
CC.
The rest of your list could use a bit of work. A sword lord, or avatar, will get left behind in this list. You really should aspire to take a mainly mechanized force. A single
cc oriented slow unit won't add much.
A fire prism, by itself isn't that useful. Really if you aren't taking 2 or 3, you'd be better off with a Night Spinner.
Since this is such a low point game, its really in your best interest to put as many guns on your troops as possible. With doom support, you'd be suprised at how much hurt a squad of
GJB can actually put out in low point games.
to demonstrate what I'm talking about, I'd suggest running a list like this
Farseer- Runes of Warding, Doom
you know what doom does, but runes of warding denies his demon prince warp time.
10 Banshees-exarch, executioner, acrobatic
Wave Serpent-
EML I understand why you want the underslung cannon, but dropping it lets you fit in 2 war walkers later. 2 shuriken cannons > 1
2x 3GJB w/ Warlock- cannon, spear, destructor
this squad is not to be underestimated in low point games. Its quick, versatile, and can shoot holes in most things. In lower point games there are less enemy units to shoot at you, and you can generally keep them hidden until they unload on something
2x War Walker- 2 shuri cannons
War Walkers are always a solid addition to a low point army. They are cheap- these are 40 a pop. And give a lot of heavy weapons fire. They'll knock down rhinos, and force D/Ps to make armor saves like nobodies business.
A list like that would give you a similar theme to the one you posted while ramping up the amount of fire power on the table.
His list doesn't seem particularly hard, with only a single rhino, likely filled with Zerks, and no obliterators, you should be able to beat him with any all comers list. Remember as long as you aren't shooting at plague marines, you'll do some real damage to
MEQ with doom + 4
tl shuri catapults, 2 shuri cannons, and 2 destructors. Don't underestimate what
GJB can do when they combine their fire on a unit.