Yep. I thought there were similarities. But Sonboly wasn’t a rightwing extremist like behring. Somewhat mirrored him but unlike Behring wasn’t espousing any particular ideology.
Something I read said that he seemed to be very interested in learning about other mass killings, particularly the Columbine shootings.
I most certainly do not have any sort of knowledge in such matters, but I suspect that he was just seething for a number of years, enduring some real insults but mostly merely perceived insults, and planning some sort of way to go out in what he perceived as a blaze of glory. Tacking on the disgusting “allah is great” was just a stylistic flourish.