Should have got your mate to put his foot down! I found it's louder under load, and near standard when not...
This is the first time I've heard of a non res being too quiet - I've heard of people changing out the rear system for a resonated system and being disappointed. For sure the car is very quiet as standard - I thought the non-res system gave a bit of voice to mine and made the exhaust note a bit deeper without being intrusive.
I think when I fit my Miltek DP I will change the rear to resonated as otherwise it will be a bit too loud to be discrete.
Still, it varies person to person. I saw a Revo demonstrator ED30 at Donington which must had had a full system as it bellowed in a very deep way went it went past the pits, but in comparison mine is a bit deeper sounding than standard although a bit muted without a DP.
As said before - some people have knocked out the pre-cat material to make a bit more sound without changing the downpipe.