We need to be careful to distinguish between "top end" overhauls and leaking valves.
Top end overhauls include new pistons, cylinder honing, conrod bearings and valves amongst numerous other components.
Jabiru valves cost $45 versus $285+ for a Rotax valve. Lapping in some valves on a Jabiru at a few hundred hours whilst not ideal is not of major financial disadvantage to an owner, but it's not a top end overhaul.
CASA comparing Jabiru failures to Rotax is floored given the reliability of the Rotax. It's a high bar to jump.