My folder isn't a Brompton, so I was forced to learn to service it myself because I literally couldn't get it serviced right. After two different services it nearly rattled apart when two different bolts weren't tightened, and the final straw was when I took it to a shop that sold mezzos, and they replaced the rear wheel and rear derailleur (16" folders go through a lot of those!) but didn't adjust the high/low screws which could have resulted in a serious accident. If I have to spend time checking they have done their job properly, I may as well save £100 and do it myself.
Is it? That's only an average of 25 miles/week. Which is respectable, but not quite "wow" worthy.
I did the maths. 2,000 is the equivalent in terms of wheel rotation and thus wear as 3,200 on a road bike. That plus how close the cassette and chain are to the dirt probably means it was due for a replacement.