Your phrasing makes it totally HR worthy to my mind, especially if the only thing justifying keeping him (experience) is not there.

I was going to give you more advice, but actually here the only one that matters : get counceling/coaching help outside the company, with someone specialised in work related topics. You need someone on your side, to listen, give you fact based advices, discuss strategies, challenge you. It's a very stressful situation, get all the help you can!