I can't speak for aikido per se, but in many ways slow training is more difficult or at least more involved, both physically and mentally.
Physically because it is like doing a pushup slowly. You demphasize momentum, thus increasing sensitivty to all muscles changes and forces.
Mentally because now you are aware of sensitivity. Which finger touches first, the temperature of what you are holding, the sensation of the mat on your toes, and probably thousands of other variables that typically rush by unnoticed when moving quickly.
And all this intense observation from a person who does not do aikido ne?
As for me, slow aikido is only when used for teaching noobs the kihon, My answer is that it is a snorefest for me. I'd say bring em on you Pansies!