Will ANY Hokages could protect Konoha.
Even Tsunade failed and went straight into coma.
3rd Hokage lost to Orochimaru.
4th Hokage also failed.
Hagoromo descendants are on whole different level.
Itachi words to Naruto about Hokage;
"Hokage ..........."
As Hokage is to protect AND Die protecting Konoha.
It was because Kakashi DID protected the Shinobi, and
Hagoromo DID commented to Kakashi that ......
So, Kakashi is the 6th Hokage for some reasons;
1. Leader of the Team 7 that protected the Shinobi.
2. As Hokage, or only Hokage can protect all Kages & Bijuu being killed - Sasuke revolution.
3. Finally, only Hokage to have that authority & power to do;
3.1. Pardon Sasuke.
3.2. Capable to elect Naruto to be the next Hokage.
3.3. And with proper handover of Hokage to Naruto.
Kishi had only given many chapters about the growth of Kakashi...