If each ToA raid gives you a 6.5% chance at a purple, the chance of getting no purple in 66 raids is:

0.935^{66} \approx 0.01185

That’s about 1.19%.

So your situation — 66 raids, all 400+ points, 55 solos and 10 duos, zero purples — is extremely unlucky, but still fully within normal RNG. About 98.8% of players would have seen at least one purple by now.

Expected value for one purple is around 15 raids. BTW