Burst pipe overnight, claim partly denied because adjuster says damage is from 'long-term seepage' - it's not

Hoping someone here has dealt with this before. We had a pipe burst in our laundry room around 2am about three weeks ago. Woke up to water across half the first floor. The shutoff was reached within maybe 15 minutes and a plumber was at the house by 7am to confirm the failure - it was a copper supply line that split at a stress point.

We filed the claim that morning. Adjuster came out four days later. Last week we got a partial denial. They are paying for the burst itself (the cleanup of the laundry room and immediate area) but denying everything beyond that - the buckled hardwood that runs into the kitchen, the baseboards, the drywall in the basement ceiling - because they say there's "evidence of long-term seepage and gradual deterioration" which is excluded under our policy.

The thing is, that area was completely fine. We were in the laundry room two days before the burst doing a full load and there was zero moisture, zero discoloration, nothing. The plumber's written report says the failure mode is consistent with sudden rupture, not pinhole leakage over time. The damage spread from the burst because it ran for 30 minutes overnight before we caught it.

Anyone fought a "long-term seepage" denial successfully? What did your appeal look like? They are saying $11,400 of damage falls under the exclusion which is most of the claim.