Brian,
Hard to know for sure, I haven't worn either out yet. Between my Howard rotovator and the Deere tiller I have tilled up about 45 acres roughly. The Deere is faster and deeper though.
I have changed out disk blades that were cracked on the small light 3 pt disks though and that can be a good sized job. These cheap disks have thin blades that don't penetrate the ground well and are easier to break or crack.
I might add that if were talking even money I would rather have a new $3000 dollar tiller than a new $3000 dollar disk. Bear in mind the OP has a Kioti 45 hp tractor not a large heavy field tractor. He has a much better chance of utilizing the pto to get the power to the ground than the wheels with traction.
Now if you have a good quality offset disk and a good disk harrow and a larger frame/weight tractor this may be a lot closer to discern the difference. Add yet another implement like a chisel plow and the scenario changes again, way cheaper implement than either a tiller or disk.
From what I have gathered most people here have small tillers with shallow depth abilities and seem to assume that a tiller is only good enough for a small garden plot. Alot depends on the tiller as to what you can do and the same is true with a disk. I have pulled a cheap disk over land before that it would take a bloodhound to follow it and pulled a heavy offset disk over the same ground with good results.
My point to all of this is I fail to see where a disk is so much faster to complete the job than a tiller. I think for similar results the time should be about the same.