Purpose is to reach the best possible file and image quality, always. This being said, I would suggest you to double-check such claims by yourself:
- ISO performance: I have posted samples of ISO 800 regarding the eMotion 75 back, months back, and I don't think it can be compared as to "poor performance". Have a search and check by yourself.
- Live view on the display of the back is simply not possible with the CCD technology. However, tethered live view works well and is not described as a "joke" by customers using it.
- Battery performance: it seems that you do not have the right information here as well. eMotion backs, with their special power management, can take up to 2000 images or 3 to 4 hours shooting with a full battery charge.
Best regards,
Thierry
so it is for purpose that we have
- poor high iso performance
- a live view which looks like a joke compared to canon and we can not even dream about live view on camera
- have to buy a lot of batteries to get through a day of shooting because of the high power consumption