It is impossible to issue a blanket ruling that would cover all hypothetical interactions or Robot designs. This is the type of question that is why VRC utilizes human Head Referees who can observe the context of a specific Robot and/or Match to provide a judgment call when needed.
G13 states the following:
< G13 > Offensive Robots get the “benefit of the doubt”. In the case where referees are forced to make a judgment call regarding a destructive interaction between a defensive and offensive Robot, or an interaction which results in a questionable rules violation, the referees will err on the side of the offensive Robot.
The Note in G12 states the following:
Note: A Robot which has expanded horizontally in an effort to obstruct the field, or is legally covering the top of a Tower in a solely defensive manner, should expect vigorous interactions from opponent Robots. Damage that is caused by opponent Robots pushing, tipping, or Entangling with them would not be considered a violation of <G12>. Gratuitous damage or dangerous mechanisms may still be considered a violation of <R3>, <S1>, or <G1> at the Head Referee’s discretion.
The first portion of this Note does not require a "solely defensive manner", it simply requires the Robot to have expanded horizontally in an effort to obstruct the field.
In the context of these rules, specific mechanisms or Robots are not assigned "defensive" or "offensive" roles. It is interactions and strategies that are assigned "defensive" and "offensive" roles.
There are scenarios where a primarily offensive mechanism is used defensively (e.g. an intake being used to entangle an opponent). There are scenarios where a primarily defensive mechanism is found on a Robot playing offense at any given moment (e.g. this video which has now been referenced on the Q&A three times).
When making a G12 or G13 judgment call, Head Referees will need to look at the specific interaction at the moment it occurred, alongside any relevant context (such as previous interactions or strategies of those two Robots).