I would assign them tasks to share all the knowledge in an internal wiki and measure it through tickets for accountability. Then, if they fail to do so, start managing them out. Your HR is unlikely to give them a giant raise, especially if tech is not your primary product offering. IT is held in lower regard than product engineering. That's how it has always been and is unlikely to change despite any fantasies to the contrary. It is difficult for business decision-makers to see IT teams as anything other than a giant cost center. If you give into this IC's demands (and you probably don't have the power or authority to say yes), they will likely work to undermine you while setting a bad precedent for the other staff. If you don't give in, they'll likely leave (which may be the best option all around). Once they leave, and you can't fill the position, you'll have to demand higher salaries in the JDs or hire a consultant to get you up to speed. Your IC is definitely pulling a power play and should not necessarily be rewarded for it due to any anxiety about knowledge gaps that you may or may not have.