2.
Current KE rules state that verse needs clear correlation between power and speed
if feat in question is carrying small objects(like lifting small sword at relativistic sword). And we don't need to prove such correlation if:
a) Character uses fast moving object to attack
b) Character moves large objects at great speed
c) Character throws object to attack at great speed
We argue that legs that Mettaton summons are linked to his actual legs, but they are distinct from them. When he uses legs for attack, we can see that his acthal legs aren't moving at all. When he uses heart to attack us, we can see his actual heart attacking us, and Mettaton comments on
this fact. If we accept that Mettaton summons 12 ton legs to attacks us, we automatically satisfy exceptions above, so we don't need to prove clear correlation between power and speed. (I don't want to seem rude, but I think question whether Mettaton uses his actual legs or summons legs isn't jurisdiction of CGM, but should be handled in CRT, since it's about specifically inverse question).
Edit: You can obviously argue that we should be more stricter with KE rules, but it should be handled in staff discussion, not here, since it would affect almost all verses on site