While I do give cbd for other reasons and have known it to work well for some mild pain related situations I would not use it as a sole pain relief option.
Also depending on why you are looking for pain relief you may be better off using Rx pain relief from your vet.
I personally have used a product called stop the pain(stp pellets) and saw good results but the senior mare still needed previcox in the long run.
If I remember correctly from other threads, there has only been one study on CBD use in horses, and the study involved one horse. So there is really no way to know if it is harmful or helpful, and what other issues it might bring up. One thing we know is that in mammals where CBD has been studied, it decreases gut motility, which in horses might be playing with fire since they can colic so easily. I wouldn't want to use anything that would delay the processing of food through the intestines in a horse.
The Tylenol sounds interesting, but a 10 gram dose (10,000 mg) would cost about $2 a day (if one 500 mg pill is ten cents) and involve giving 20 pills, which makes me wonder why a person wouldn't just use Equioxx, which costs about $1.40 a day and involves one small pill, and we know it is very effective for pain and inflammation in horses. My gelding has been on Equioxx for a couple of years with no side effects that I can tell.