I understand your frustration - it will not affect your sales - your response was polite and professional buyers will read your response 

However it might be worth ringing ebay in the morning and speaking to Dublin - ask the cs why the feedback cannot be removed under the feedback policy - You could try arguing ' The buyer is raising an issue that was correctly disclosed in the listing' On the basis that you disclosed specifically that it was not a 100% essential oil because it could be an issue due to similar products being sold that are 100% essential oil  therefore the issue was pointed out in the title and description   - it's a long shot because this removal I guess is aimed at items with faults pointed out - worth a try it might work ? 

- see below

Harmful, inappropriate or irrelevant comments and images
We remove all feedback that contains any:

Content promoting hatred, violence or discrimination
Profane, obscene, adult, illegal or explicit content
Opinions on any political, religious or social issues
Any implied or explicit threats or intimidation
Personally identifiable information
Links, URLs or other content encouraging sales outside of eBay
Infringement of third-party rights
Meaningless content or images that aren’t of the item purchased
Comments intended for a different item or seller
Negative comments with positive ratings, or positive comments with negative ratings
Personal attacks that could harm the reputation of the seller or their business and could not reasonably be viewed as constructive criticism
Any pictures left in feedback should accurately represent the item purchased and follow our policies, including the Images, videos and text policy, the Offensive materials policy, the Restricted adult items policy, and the Illegal explicit content policy.

See example

Extortion and manipulation
We remove all feedback that:

Is used as a means to extort another member
Is used to manipulate feedback ratings (see our Feedback manipulation policy)
See example

Buyer-related transaction issues
We remove neutral/negative feedback when we can see that:

The buyer asked to cancel after placing their order
The order was cancelled due to an issue with the buyer’s address
The order was cancelled because the buyer didn’t pay
The buyer is raising an issue that was correctly disclosed in the listing
The buyer has been actioned under our Abusive buyer policy
The buyer requested a change to an order after they’d paid (and their feedback relates to this)
See examples