Crank/blade damage or lack of doesn't mean the flywheel key hasn't been sheared. It runs so it hasn't been knock out much if it has but it could be off just a little and that changes ignition timing. Most times with Briggs you don't need to remove flywheel to inspect. Removing flywheel retainer and washer or cup allows you to look down on end of crank and see the slot in both crank and flywheel to see if they are still aligned.

Bob