I would tend to support your friend's approach, although I have more lenses. His choice is excellent IMHO.
When I travel and have enough luggage space, I would aim for a 4 lens kit consisting of:
- an all-around zoom lens (DA18-135mm or DA18-250mmm/DA18-270mm)
- DA15mm
- Voigtlander Nokton 58mm f1.4 or FA31mm f1.8 Ltd
- FA77mm f1.8 Ltd
Good quality prime lenses have outstanding IQ and do give me a higher keeper rate. Thus I like to have as many primes as I could, although they lack the versatility of an all-around zoom.
As you can see there are two common lenses between your friend and my list.....
My 5 cents.