I wasn't familiar with the Bullet Cluster[0], but as you described it made it very interesting. I'm no astronomer, but from all of the examples of gravitational lensing[1] I'm familiar with have a very distinct look that I'm just not seeing with the Bullet Cluster. Where is the lensing effect occurring that is leading to this theory?
Gravitational lensing doesn't have to be apparent to the eye as those extreme examples on the wiki page are. The second image on the bullet page shows matter in pink and measured lensing in blue.
[0] https://en.wikipedia.org/wiki/Bullet_Cluster [1] https://en.wikipedia.org/wiki/Gravitational_lens