I have used TPLink Deco’s for this application before, they have now become my default go-to multi-purpose tool when a family member asks for advice/help and keep a few 2 packs handy for such occasions. I can’t remember if it was the X20 or the X40 when I tested it, but the best iperf results I pulled were just under 800mbit between nodes. Obviously, that depends on what you have between nodes (physically) and what standard each node supports.
An extra Atlas Pro isn't that expensive, especially used, and as you have found, having to mess about and compromise often leads to more time and effort being expended than is justified by the potential saving. Regret and compromise are unfortunately often expensive bed fellows.