All absorption silencers will need repacking at various stages to maintain their efficiency. 5000 miles doesn't seem a lot to me.
2.5kg for a twin silencer system is impressive, especially including the link pipe...given that the LV system weighs close to 9kg and is also ally.
My single titanium race silencer weighs in at 1.4kg, so I'd check that they aren't just weighing a single silencer.