cant say the 4k looks any sharper than HD on my 2.5K LCD.

Market expected that customers would react favorably to the new devices and many of them did but things are expected to change in this quarter as industry watchers believe sales of the Galaxy S6 will actually fall short of expectations in the second quarter. The apprehension continues to mount as we head into the fall where traditionally Apple launches new iPhones and that’s also perceived as a threat to sales of the Galaxy S6.

Securities industry sources cited in a new report suggest that Samsung Electronics’ IT and mobile division is going to post an operating profit this quarter between $2.76 billion and $3.03 billion which would be a 22% increase quarter-over-quarter but a 24% slump year-over-year. This performance is attributed to low actual sales of the Galaxy S6 and with hopes for the next quarter being pinned on the Galaxy Note 5.

Huh

considering its 4K is not any sharper than BMPCC's raw HD

Well, I do not know that sharper means here. You better go and check reviews with actual measurements.

Another review

Galaxy S6’s image quality is nothing short of miraculous. Its 1/2.6-inch sensor size is marginally smaller than the 1/2.3-inch sensors in an average compact camera, yet the S6 is still able to resolve an impressive amount of fine detail in close-range subjects, and manages to avoid smoothing foliage detail in distant landscapes. Colour reproduction and exposure metering are also first class and the camera produces beautifully vibrant and accurately exposed results.

https://www.ephotozine.com/article/samsung-galaxy-s6-review-27831