I just have a hard time seeing Reigns not being #1 in kayfabe. Look at his reign still going. Bloodline is THE storyline. Wouldn't be surprised if Gunther hopped MJF, either, but Roman's lack of matches and ring work are the only things holding him back from Gunther or MJF hopping him. I wouldn't be surprised if MJF or Gunther are #1, either, as that would be personal preference but it's not 100% what I want as a top 5. My personal top 5 would look a lot different.
I would go further than you and say BOTH MJF and Gunther are old school in ring work, making them standout against a sea of spot monkeys and puro strikers.
It still blows my mind that Gha-cha-ping of Z-1 broke the HTM's IC record.