The edges of wood boards always warp into the direction where the bark was, i.e. into the direction of the surrounding forest. Look at the annual rings. As far as I can see in the picture the rings of the tail board have their radius inside the cabinet. Just flipping the tail board over would surely have minimized the effect of these forces.
If there are no rules, cheating isn't defined.
If it is a contest to show pure hand skills, it is cheating to use a jig that was made with powertools, if there was a rule against this.
The discussion reminds me on rock climbing. There is a so called "redpoint" climbing style, where it is forbidden to work against the gravity with technical support (e.g. iron hooks as "jigs"). Technical support is only allowed to be safe in case of fall (harness, rope, carabiner,...).
Btw: If the client pays good, use anything to make it look good and durable and to finish quickly.
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