I feel that Riptide Retreat should be about 3-4 laps (leaning more torwards 4) As it is a generally longer map compared to the rest of the maps and I feel it world fit better. I took me 4 minutes to do 5 laps on riptide retreat while on other maps it takes me around 1:45 to do it.
Also the top times are drastically longer then the other ones to show the comparison.
Riptide Retreat
Pine Valley