Blasters and Blast Pistol are your only anti armour. Personaly I would go Dark Lances on the Raiders and then give Agonisers to all who can take them (Power Weapon in the hands of S3 needs 5s+ to kill T4
).
You loose the AP2 weaponry but your Archon and Whyches with their inv. saves should be able to take on most elite units in
CC who have good armour saves. Your Warriros should be 10 and your Wyches 9 so your Archon can travel with them. Warriors are for shooting, so debus into cover, if you didn't start there already, and use their Raider as anti tank killer. You have already given them my 1st choices; Blaster and S.Cannon.
My first choice, if any, on Wyche weapons is the hydra gauntlets for those extra attacks, and the Stunclaw on the Hellions I think is over rated, but give it a go, let me know how it works for you. Again, as I said earlier, he would be better off with an Agoniser.
First choice also for my Archon is the 2+ inv save. Expensive but with the right dice rolls he can go on forever
At T3 your Archon with Ghostplate Armour will suffer Instant Death from anything S6 when he fails one 4+ save, forget power weapons. Did you not take that option due to your opponent having Necrons and the Lord's Warsythe not allowing inv. saves?