You have a point that some drugs and their isomers and esters are controlled, but in this case the ethyl Ester is very likely uncontrolled.
For example, MDP2P and its salts and esters are on the List 1 chemical list, but imo, the ethyl Ester does not fall under this. It is the ethyl Ester of MD phenyl aceto acetate, not of mdp2p, and it isn't an isomers, as it doesn't have the same molecular formula.
There are a few little bits of wiggle room here or there, and while this doesn't stop the arrest, it may allow a lawyer to beat this in court.
However, I'm not a lawyer, and could be completely wrong.