Oh, in this case...
Faramir and Boromir's leadership when they reach the adequate level are also negated by heroic statues, Elrond also when near a Pavillon of Tranquility, Thranduil also when near castle's statues, even King Dain burst of rage of 100 % damage when in combat is negated near heroic statues.
The same problem occurs near Lake-Town and Dale with Mayor Lodge for example.
I am under the impression that statues negate all hero's leadership.
Are not negated however :
Some active leaderships such as :
-Durin's word of Silence
-Lothiriel Heroic Resistance
Some bonus effect such as :
-Rallying call (tested it with an individual unit level 1 attacking a ruin near a freebuild heroic statue)
-Dwarven Last Stand Central power
-Golden Eregion arrows buff (very hard to test but pretty sure)
Those 5 effects are not negated, but all passive leaderships seem to be exclusive of heroic statues buff. Not that it displeases me, less cumulative leaderships means also that Nazgûls are not such insane f****** when they come, more balanced then, the problem is just that heroic statues then can be annoying because their effect persist for 30 seconds if for example they deter Dain from triggering properly is burst of rage.
If the current state of heroic statue would continue, they should not apply their effect after being destroyed or at least offers an option, an ability such as reinforcment for wells that would allow or disallow their leadership to persist after leaving their range or after the statue being destroyed.