I don't understand how anyone can be certain about that. Rogla is so far ahead of non-Slovenians (as we saw in the Vuelta last year), and while he appears far more vulnerable than Pogi, his top level is stratospheric too.I don't really understand the need to compare Roglic to Pogacar.
Pog is a better and stronger rider overall. Expecting Roglic to win the Tour riding mano a mano against him would be kind of irrational. Which is why I believe Jumbo's strategy to go with 2 leaders makes sense, even if it probably won't work.
We've seen them head-to-head in top condition in the first two stages of the Tour last year, Itzulia before that and the 2020 Tour. I did not see Rogla unable to put up a fight.