Sage Centipede took multiple attacks from Garou, and couldn't believe how powerful Garou actually was. The second he could, he took a hostage to prevent Garou from moving. This already tells us everything, Garou was "too strong" and he wasn't fully confident in dealing with him without some kind of insurance.
Once again, Sage only directly fought Garou when he had no choice. Hostage was impossible and there was nothing else he could do. Garou was already scaling to Sage from the start, and trying to ignore that is unacceptable. Saying that Garou being unable to break Sage's feelers doesn't mean anything, they can be however durability the scaling says.
Only reason we can say his feelers are less durable is head canon. But this is fiction, anything can be as durable as it wants. I know of a character who's index finger is more durable than any other part of their body. And that isn't even their power or anything, just something random.
If Garou was only 6-C and Sage had an attack that was hundreds of times more powerful, why is he afraid of Garou and wanted to take a hostage to keep him from moving? I heavily dislike assuming characters are stupid just to fit our head canon scaling.
Sage believed Garou's strength was "too strong", and was not confident in fighting him without a hostage. Always trying to take a hostage, until it became impossible. There is no getting around this fact, which means he didn't believe he can defeat Garou in one hit like your scaling is suggesting.
Since 51 Gigatons is many, many, and many times inferior to 2.4 Petatons.