Also why did they not build a static rig at T5 which could have helped this chaos considerably?
At Charles De Gaulle they used to have two static rigs, one of them blew down and they dismantled the other. They were a real pain to use. For a start you had lines of aircraft queuing up with engines running waiting to get onto a rig and they were also positioned some way away from the takeoff point, so you ran the risk of running out of holdover time* before you could depart. Static rigs put all your eggs in one basket, rig goes down all is lost, a deicing truck goes down then you may have lost one of 20.
The real debate is between on stand and remote deicing. On stand is flexible and cheaper but you do have the potential hold over issue. Remote deicing accomplished by a team of vehicles at a location close to the takeoff point is operationally more desirable. It is also flexible in that you can allocate resource depending on aircraft size, e.g. 4 rigs for a widebody, 2 for a narrow body, to keep the flow going. It is however expensive in terms of manpower and equipment. It is the better option if you have lengthy and forecastable periods when deicing is necessary but (Northern Scandanavia) but in more temperate climates the decision is much less clear cut.
Sorry, but no easy answers.
YS
*
Holdover time Deicing treatment is only effective for a finite time after application. This can range from a few minutes in very low temperatures with heavy precipitation to hours when the temperature is just below 0degC with no precipitation. The type of deicing fluid used is also a factor. Crews have table that combines these factors and enables them to calculate the "Holdover Time" for which the deicing treatment will remain effective and keep (primarily) the wings free of snow/ice. If takeoff is not accomplished before the holdover expires then it back for further deicing. Here is a little more from
Wikipedia about it.
Hope that this helps.