Thank you for the detailed write up.
I did just give my JF rings (before reading you post, but would have anyway) ahead of GM II.
a) I defended him on the forum and feel I should put my money where my mouth is because I DO believe that he fills a role for me and I will find him useful.
b) He has an ability no other hero has that I value (defense down flip).
c) I use the avatar and love it so thought it is only fair.
I do NOT expect to use him on main raid team but I don’t use GM +10 either.
I would try him on main raid team if his DoT were extended to three turns at the same damage per turn (getting onto main raid team is not easy, 22 5* and 40+ 4* to compete with, so I make this statement as a positive endorsement of JF).
He WILL be very useful on my war teams and the defense flip should make some last flag attacks much easier. He will be very useful against any riposte and defense down enemies, mostly that applies to Kunchen tanks in wars, the occasional Boss Wolf shows up too.
As you stated, JF’s special does not benefit from the defense down heroes and his tiles are middle of the road for a 5* which makes the pairing with G Falcon and Wilbur is less appealing. That said, FEW of the red heroes have really powerful hits. Marjana is the big sniper in red and her damage is on the low end of the fast snipers.
JF does his thing on his own, he isn’t improved by many other heroes and simply makes his contribution and carries on. The burn is legit and helps knock health down to sniping range, the defense down reversal is solid. I say that from having faced him in raids, I needed to fire Kunchen to save my team and cleanse, the defense down flip certainly saved the enemy from death by tiles and/or specials. It isn’t a win button but it improves the odds for JF’s team.
I LIKE him, I don’t love him.
(Edit): I would also give Grazul rings before JF. I adore Grazul. Sadly, that is done from a “social” distance because she did not grace my team.