Ah, I misunderstood your comment. When you said it was competitive with the 6900 XT I thought you were talking about GPU performance in general, not just in terms of memory bandwidth.
According to the numbers Apple is touting, the M1 Max is competitive with modern GPUs in general, being on par with—roughly—a 3070 (laptop version) or a 2080 (desktop version). They've still got a ways to go but this is shockingly close, particularly given their power envelope.