How should “fit for defense but not imposition” be understood?

Argument Without New Proof: Absence of a Cause and Presumption of Continuity

• Istishab both preserves existing status and establishes all new financial rights
• Defense merely ends disagreement, whereas imposition merely states a rule
• Istishab is weak for defense but stronger for new entitlements
• An existing right may be defended, but new entitlements are not thereby established