It's probably a good idea to acquaint oneself with 35mm cropping/framing in general before making any sweeping judgements.

There's a fairly lengthy discussion about it here. The quick version is that cropping isn't a binary thing - cropped vs. uncropped - but rather a sliding scale affected by a number of factors from photography through to printing through to projection (and more if video transfers are factored in).

Cropping is right and proper, because you aren't supposed to see every grain of information on the 35mm frame. TServo2049 posted some excellent comparison frames in that thread which show the SMPTE aperture standards - 5% and 10% - and their effect on the 35mm image when properly projected.

The new 35mm scans being used will certainly need such cropping, unless the intention is to show parts of the image that were never expected or intended to be seen. I expect that the effect of the curved mask on the Blu-ray footage is also comfortably within that 5%-10% range, since it's a fairly conservative scan.

So, is this an accurate preservation of every possible piece of picture information in ESB? No. Is it an accurate preservation of a projected, cinematic experience? Yes, and though that won't be enough for some people, I for one am very happy with it.