Galacta Knight nearly cut it in half, doing more damage to it than the Robobot Armor in Halberd Mode did over the course of an entire battle with a single stroke. It's pause screen description in the True Arena states it activated a new program. The scenario seems to me more like it came back from the brink of total destruction than actually tanking Galacta Knight's attack. Make no mistake; while it ultimately survived, Galacta Knight did huge damage to it, and with just a casual attack, no less. Hence while I'm hesitant to scale it's durability.
I'm not sure what makes Whispy Woods City-Block level. I simply scaled Star Dream's base form to the size of the Halberd, which is admittedly rough at best since the Halberd apparently does not have a consistent size from game to game. Sure, it's above everything else in Robobot (except maybe Galacta Knight), but I'm not sure how much that counts for. We've got the Robobot Armor which can casually punch out cars and buses, but other than that, I don't recall anything else notable in Planet Robobot itself, and I'm hesitant to pull feats from enemies in other games because of the series' inconsistent nature.
Scaling Galacta Knight to Kirby and co. in the way you seem to be implying (MSS Galacta Knight) requires ultimately scaling him to Claycia/Dark Crafter simply because Kirby fought both of them, which is faulty for reasons I've stated repeatedly.
Pause screen description states the Robobot Armor copied Kirby's ability to copy the abilities of his enemies. Nothing to the effect of Kirby actually making the mech more powerful, though Kirby does seem far better at using it than his enemies. And scaling it to Kirby runs into the issue of "Kirby in what game?" because Kirby's showings vary across titles. Are you suggesting it scale to Claycia or Dark Crafter?
As for base Sectonia, the best she has going for her to my knowledge is scaling to an amped Kracko. Granted, I just said I'm hesistant to pull feats/scaling from other games, but I'm willing to make an exception for Kracko because he appears so often and mainly because the pause screen description heavily implies he was being amped by Taranza, as well as the fact that he has several new and powerful attacks. From there, it just remains to be seen what Kracko should be rated as. He either scales to Kirby blasting King Dedede out of his castle or the Megaton Punch characters/feats.