Taxi queues can vary by time of day and terminal, there’s a couple of times I’ve seen long queues this year - usually after a long weekend (in SG) , but I can’t say how long as usually I will take a Grab (SE Asia’s Uber) from the airport. Strong correlation between taxi queue length and Grab wait times.
Having said that if arriving in T2 or T3 the MRT is still a reasonably quick way of getting to central areas, it certainly wouldn’t add an hour to the journey time, maybe 20-30mins depending on how far the destination is from MRT stop. If arriving in T1 you have to add 5-10 mins to take the sky train and walk to the MRT station and from T4 l, well unless you know what you’re doing Taxi or Grab us certainly much quicker.
Having said that if arriving in T2 or T3 the MRT is still a reasonably quick way of getting to central areas, it certainly wouldn’t add an hour to the journey time, maybe 20-30mins depending on how far the destination is from MRT stop. If arriving in T1 you have to add 5-10 mins to take the sky train and walk to the MRT station and from T4 l, well unless you know what you’re doing Taxi or Grab us certainly much quicker.