Yeah, the thing is, I don't think he would think of her as an extremely weak adversary, or an extremely strong, either. In fact, Kiyotaka admittedly doesn't form his judgment upon hypothesis, and doesn't speak without certainty, in serious situations at least:
(Source: Chapter 19 from the Year 2 COTE manga)
(Using a manga scan feels illegal, so yeah
(Source: Year 2 Volume 1)
In Year 2 Volume 4, during the fight with Tsukishiro and Shiba, his immediate analysis wasn't hypothesis about Tsukishiro and Shiba's power levels, but environmental analysis, and the possibility prediction of the boat driver being a possible ally with them, or about them having a possible concealed weapon.
In fact, even after fighting them, his intuition only thought of their clear power levels (which were much lesser than his own, to the point where he was still thinking about taking any of them in a single one-shot, meaning that he still didn't clearly "overestimate" them):
(Yellow: Represents Kiyotaka's processes done purely through intuition. In all the conclusions drawn through intuition, the analysis formed doesn't put either of Tsukishiro and Shiba above him.
Green: Represents that Kiyotaka hadn't dismissed any possibilities regarding the differences in Tsukishiro and Shiba's power levels, while simultaneously having the information about the levels of at least either of them.
Light Blue: Represents that Kiyotaka was still thinking of the one-shot plan he had thought of before. Yes, Kiyotaka was actively thinking about a plan where he took one of them in a single hit, and then fight with the other. And his opinions on being able to one-shot still hadn't changed much, even after the revelation of his opponents' abilities only being better than before.)
However, I wouldn't go on outright voting Kiyotaka off these. These only prove that Kiyotaka wouldn't think of Princess as very highly even in the first glances and wouldn't form analysis which are impractical.
How strong is the Princess in deception? Like is it just plain lies? Or are they some kind of mind-hax?