Do you think LI's problem is innate to the platform, or it's users? How will an alternative professional social network make itself immune to the scourge of online 'business networking'?

I honestly believe the problem is inseparable from the social network itself. Either you have a space where people can connect and find jobs and nothing more, and you'll have zero engagement and no way to really fund the platform. Or you allow actual social networking (i.e. public posts) and then open yourself up for lots of engagement, and all the associated cancer that comes with that.

Users reflect the platform. You make reddit, you get echo chambers. You make 4chan, you get edgy contrarians.

Users that thrive in those enviroment stay, others leave. LinkedIn is a scourge to the job market, being force to publish your entire life for everyone to see to find a job is completely dystopic.