Jarrod isn't irredeemable, just not when he is still in power and still gets what he wants. And you can't romance him if he loses power because he resents you for it, which makes sense as what he feels about an MC that romances him is closer to infatuation than true love.
What I think is the problem here is that the game doesn't indicate you are maintaining a relationship with Jarrod after you get the golden ending for him and Revaire. After all the effort to redeem him, he isn't mentioned as your friend during the friendship section, which is unrewarding and gives players less space for a post-Summit romancing Jarrod headcanon.
I'd love to see Aly add a friendship section in the epilogue for Jarrod, but the game is already so massive and took so long to make, requests should be made in moderation.