Do you think Sun believes he bought Steemit, but not Steem?

IMHO the branding of Steem and Steemit is very confusing and it combined with the large ninja mined stake may make anyone think they can control everything steem. Graphene chains have given emphasis on governance from day one. The philosophy is quite difficult for those who are new to the platform to understand.

As the purportedly, largest holder of Steem, is that good or bad?

We don't have smart contracts enforcing various promises put forth by the white papers, roadmaps etc. Beyond few basic structures and social "honour" contracts there is no enforcement. How new stake holder(s) will use is thus completely upto them. I said holder(s) and not just holder as TRON foundation may have some voting and decision making process of its own. I have no idea how TRON (foundation) operates.