ADE, the Desktop application, provides a subpar reading experience, to put it midly. There are far better software for the user that may want to read their ebooks in a desktop computer, so one should not expect anyone in their right mind to be using it for that purpose. The uses of ADE that one can expect, then, come down to:
1. Being able to sideload DRM'ed ebooks to your ereader if your ereader vendor did not provide something more appealing, in which case, the quality of its reading engine is irrelevant.
2. A way to test how ebooks will look on an ereader that uses Adobe's RMSDK reader, which most eink based ereaders use and then some non-eink.
Considering that even if Adobe updated their RMSDK, one should not expect even 1% of ereaders out there being updated, having Adobe release only incremental fixes to RMSDK would actually be worse, not better, for ebook producers, as, if anything, one can today get an approximate idea of how bad ebooks will look with only one version of RMSDK around (well, purportedly there are several around, but Adobe fixes so little from one to another that one can obviate their differences).
I do agree Adobe should put some effort in the embarrasment that RMSDK is today, but for the love of god, do only release a new version if the whole reading system has been rewritten from the ground up to be up to today's web engine standards. If they are going to only fix tiny little things, like not blowing up as soon as it finds a media query, please do not bother: we are already bad enough with one single coherently crappy standard reading system.