Everyone should be able to agree that favouring Johnson requires a leap of faith. You have to assume the skillset we see him possess is a good enough skillset to overcome fighters we can see at the top level. We can see Dempsey against Gibbons and Willard. We can see Frazier against Foster, Quarry, Ellis and Ali We can see Marciano against Walcott, Charles and Moore. We can see all 3 against elite opposition. We cannot say the same for Johnson. We can see him against lesser opposition and we can see that in theory he has a style advantage but it's then a question of whether you're willing to assume he would be able to keep that advantage at a higher level. No need for petty insults it just comes down to how good you think Johnson was capable of being. Similar to Dempsey ad Frazier. Dempsey looks quicker, more elusive and harder hitting but Frazier is proven at a higher level. Were Dempsey destroyed Carpentier, Frazier destroyed Foster. Were Dempsey bullied Gibbons, Frazier bullied Ali. Were Dempsey beat Willard and Firpo, Frazier beat Ellis and Quarry. So yes Dempsey looks superior on film to a certain degree but would he have looked that good against the opposition Smoke faced. There is enough evidence to make an educated assessment of each fight, but you do have to be willing to have that leap of faith with the elder two imo.
How good Johnson was capable of being? He was rated the greatest hwt champion for a reason. His defense was phenomenal and very well suited to handle fighters like Frazier and Marciano. He would tie them both up in knots.
Marciano and Frazier could win a decision from JJ I suppose just from activity. However, I have a feeling that wouldn't happen. Johnson loved shorter fighters who would press him, he feasted on them. I have no doubt Johnson would look the better the fighter, and land the harder precise blows. My only concern is Johnson playing it too safe and getting outworked for a decision. If the handcuffs are off... he wins
I'm willing to give JJ the benefit of doubt and say he could replicate his skillset against much more elite opposition. I say he takes this tourney by winning both matches on points.