He beat the dragon in ch 19 on screen, which completely reversed most people's opinions on him.
The trashy adventurer group (the ones that keep mocking him) tried to make up excuses that it's because of Garm and Camille (the dragon girl), but people just mock them for their own low clearance (not even floor 20) including someone saying 'well, if it's all because of having strong allies, how 'bout you get some strong allies and do that too'
Amy in the mean time has gotten into that self-loathing mode, thinking that with dragon girl there (who can fly, have higher dps, etc) Tsutomu won't need her anymore (cuz clearly she hasn't heard of the sneaky rogue role)
Oh btw when the vice leader asked Tsutomu not to get angry with Amy, he asked her age and upon hearing 18 (he thought she's like 16) he said "Well, it would be immature of me to get angry at someone younger"
Which prompted a hilarious moment age checking and the dragon girl internally panicking at how much she's been teasing Tsutomu because she thought he's younger.
i.e. when onee-san realizes this 'boy' is a 'man'
Btw Tsutomu is 22.