The problem is that Gotenks told Buu not to do anything until he say so and Buu was standing there doing nothing at all. The fight was completely a gag fight and hell, even Toriyama admitted that.It's also implied Super Buu powered up. Piccolo thought Super Buu was ~ Gotenks and ended up to be > SSJ Gotenks, and Piccolo is not trash on Ki sensing. Gotenks and Piccolo were also in awe of Buu's power when he started to scream, and that was before the portal was opened.Power up was always stated or implied most of the time.
In Freeza's case:
Chapter: 304 (DBZ 110), P8.3
Context: after Freeza finishes his final transformation
Piccolo: “Wh-what an absurdly large ki….!”
Vegeta didn't have a chance against Freeza before their fight even begins. He's just delusional that he was a Super Saiyan therefore that makes him the strongest by default.
Chapter: 304 (DBZ 110), P10.5-6
Context: after Dende heals him
Vegeta: “Freeza’s battle power…! So he’s finally shown his true form, huh?...Well, I don’t care if Freeza or anyone else comes at me…! I’ve just now become a Super Saiyan…!”
Chapter: 305 (DBZ 111), P13.4
Context: Vegeta can’t follow Freeza’s movement
Freeza: “I get just a little serious and raise my speed, and it seems that you can’t keep up with me…Are you really a Super Saiyan?...”
Freeza raises a litle effort and speed something that Buu didn't do at all against Gotenks.
Here, before Vegeta fought Perfect Cell, Krillin told Trunks that Vegeta doesn't stand a chance against Cell.
Chapter: 383 (DBZ 189), P4.8, P5.1, P6.1
Context: after saying Vegeta will be killed by Cell
Kuririn: “It-it’s true that I’m absolutely nothing special compared to you Saiyans…B-but I can at least tell how strong my opponent is…”
There's no need for them to power up with their aura but the GOAT Toriyama will always implied it.