If you're good enough to win most/all of the time, you're going to have a high rating. And my sense is highly-rated games average far longer than 4-5 minutes. Mine average maybe 15 minutes, and I'm not playing much slower than my opponents. Update: I just won a MP game in 34 minutes when my opponent ran out of time. This isn't typical, but half-hour games are not super-rare for me either.
Let me just chime in here and say i had a party that could clear every single adventure up to 12 in 4 turns per map most cases it was 1-2 turns with a very very low failiure rate. Granted i also used to have a pvp party that finished its matches in the same time faster than any other deck at the time but if you asked me to pick i would take pve over pvp any day for speed farming.