If professional editing has taught me anything, it’s the importance of managing expectations for the client who requests an edit.
It’s essential to know that the editor is there to make YOUR text the best IT can be. The editor is NOT there is rewrite the content for you. A proofread will just make sure the grammar and vocabulary is correct. A copy edit, on top of the grammar and vocabulary, will attempt to adjust small elements of the argument and, importantly, to clarify the argument that the writer is trying to make. This may include tiny gaps being filled in. However, if the argument itself is flawed, then it is not the copy editor’s job to make a new one. It is their job to point out when an argument is flawed, but, in that case, there is little to say but ‘this needs to be rewritten’.
Here’s why. Whenever you are asked to write anything, you are being asked to express yourself. (If you want the editor to actually create the argument for you, then you need to pay them as a writer and not as an editor). This is as true of IELTS writing as it is of academic writing. The most important thing when writing is to construct a logical argument using plenty of example to demonstrate the point.
So, make sure that your point is a well-argued one. Then worry about presentation. Then hire an editor. Don’t expect the editor to fix a flawed argument.