I don’t know how 66% compare to other prediction models like the ones based on classical Machine Learning algorithms. Do you have any comparison data?
(This shows why betting on sports is almost impossible to have a long-term edge as it's already a very efficient market and the odds usually reflect the win rate very well.)
As another reference, an earlier predictor that also uses the elo rating system has an accuracy of 65.3% which is very close to the result in this post, and I guess this may be a typical range for elo-based predictors. https://github.com/luke-lite/NBA-Prediction-Modeling
By the way, I really like the interface of this "emailware". It's really fun to play with.
I'm not even considering home/away, let alone win margins, recent form, strength of schedule etc. I'm almost amazed this model couldn't make any use of them.