Sure, let me break your argument then:
None of your arguments about how the card is incomplete is even close to valid because this competition literally asks you to break rules
Make better rules next time.
Is it safer to be allowed within reason?
Yeah! Of course it is!
Maybe with reasonable challenges?
I only see 1 clear violation of the rules in this challenge.
The opening post of this challenge clearly states that card art is not allowed.
If the card art is removed then I agree completely with DM
"Don't put art in your card" is a rule
If I put art in a card I'm breaking a rule
Breaking a rule is what the competition asks me to do
Placing art in a card is fine