Balance > good design?
The new Sion is undoubtedly better designed (the old one was a binary mess) but less powerful. However, by and large, the community has rejected the rework: his pick rate is half of what it used to be and most feedback is negative.
The new Xerath now plays like a long ranged siege mage whereas the original was just a generic nuker. The community disliked the rework until the new one proved to be viable.
The new Cassiopeia actually has a niche, albeit a forced one, that of the ultra late game hypercarry, strong in a late game team comp or protect-the-Kog lineup but weak in an early game domination team, at least on paper. The old Cassiopeia had no unique strengths compared to the many other characters with near identical roles in the game, so just giving her a niche was a definite win. Unfortunately, the rework was an accidental nerf and the community spit her out.
This seems to indicate that "good design" is much less important to the community as a whole than viability. Seeing as the plural of viability is balance, perhaps the community does not really want champion reworks and would prefer it if Riot just balanced the champion pool instead?
