This is a really good discussion
I haven't read the waiver either.
But generally waivers are set up to prevent companies from getting sued from obvious risks. eg. Sorry for the go-karting metaphor. The waiver form at go-karting is not signing rights away as such. But says that you understand the risk in the activity and if you get injured from this activity you can't sue us because you have accepted the risks.
In the Essendon case, (if i was EFC) it wouldn't be written "legal drug" or "illegal drug" I would have written the name of the drug (whether how accurate the name was). Then it would be the responsibility of the player to find out from ASADA whether the drug is illegal or, in the Thymosin case, we require more information before we can say whether this drug is acceptable for use.
So by signing the waiver form without doing the research with ASADA, the player have said they understand the risks involved with this supplement program, and take responsibility of future consequences.