My hypothesis is that stronger arguments require less, if any, assumptions.

There are missing pieces in the Tigers and Mr. Fat Cat arguments. For the tiger one, assumed premises could be 'If a mammal is aggressive and can cause serious injuries to people then it is not suitable to keep a a pet', 'Tigers are mammals' and then you have the 'Tigers are aggressive and can cause serious injuries to people'. Therefore, not every mammal is suitable to keep as a pet. This follows a strong line of reasoning, similar to the Disney scenario = it is a stronger argument.