Demon Slayer: Kimetsu no Yaiba has revealed just how weak its main hero Tanjiro truly is. That's not a knock: over the course of the Demon Slayer anime's two seasons, Tanjiro has grown by leaps and bounds to become a frontrunner in the Demon Slayer Corps. At the same time, Season 2 of Demon Slayer has exposed Tanjiro (and we the audience) to what the true power of Upper Rank Demons is all about, and within that new framework, it's become all too clear that Tanjiro still has very far to go to matching the power of a Demon Slayer Hashira and their Upper Rank foes!
(Warning: Demon Slayer anime SPOILERS Follow!)
In Demon Slayer episode 40 "Transformation" Tanjiro has been battling Upper Rank Six demon Daki in the Red Light District, but ultimately wore himself out trying (and failing) to take Daki out with the Sun Breathing style. First, Nezuko unleashes her full demonic powers to save Tanjiro (but loses control), then Sound Hashira Tengen (finally) arrives on the scene. That's when we get a true measure of just how weak Tanjiro really is.
While Tanjiro nearly kills himself just trying to land the beheading cut on Daki's neck, Tengen is so powerful that he severs Daki's head in one stroke that's so fast, Daki has an entire monologue before she realizes that she's been beheaded.
Now granted, Tengen doesn't finish Daki off, either: the true Upper Rank Six power is Daki's brother Gyutaro, who shares her body with her. Gyutaro looks like he will be much more of a threat than Daki, in the final boss battle of Demon Slayer season 2.
...But back to the point about Tanjiro. While Demon Slayer has shown Tanjiro exhibiting one-of-a-kind blazes of power (see, the end of the Mugen Train battles), Season 2 has been steadily letting us know that the actual big battles the series is building to are going to be on a whole other level. Tengen, Daki, Gyutaro (and earlier in season 2) Kyojuro, and Akaza have all been clear examples that Tanjiro has a lot to learn about the demon-slaying arts before we see him unlock the true powers of Sun Breathing that clearly are dormant inside of him.
To that end, the clear gap in Tanjiro's current power level and the Upper Rank Demons/Hashira is another kind of indicator: That Demon Slayer season 3 probably has a training arc coming our way!