I think the important distinction to be made here:

It's not theft if someone doesn't make something new for you.

HIVE is a fork of Steem, but the only way it negatively impacts Steem is by being more desirable than Steem.

What JS did was basically the opposite of what HIVE did.

HIVE created new things and simply left out the people who were trying to do a hostile takeover of Steem.

Steem took things people already owned because they had the audacity to make something new.

I think we're going to see a large and successful lawsuit against Steem, but there's no real legal standing for a case against HIVE. The whole social media frontend thing is the only justification they can make regarding stealing, but the fact remains that social media posts (especially those made with the full public posting style of Steem/HIVE) are likely not going to be something a court would make a big deal over. It is, after all, possible to "delete" posts from HIVE if people want to log in and do so, and it is probably even possible to automate this process. The data remains, of course, but from a court's perspective I don't think this would be a big deal (or if it is they would need to start going after Google and Facebook for similar issues).