Just my hapence, my understanding of the reason why the “God created an old world” theory is not misleading is basically this: Hashem didn’t create an brand new world, with seeds in the ground but nothing grown, with eggs but no chickens, etc. To some extent, the new world was only possible with some level of “backstory”. The same way a fully grown lion that was created would have had to in theory be born, a fully grown tree would in theory have had to be planted, a fallen tree would have had to be felled; the entire world as a functioning ecosystem had to have a backstory.
It’s not that Hashem had this clever thought, “Let me put in some tricks to fool them!”. It’s that the entire premise requires that the newly created world paradoxically had a past. Dinosaurs, this argument goes, were part of that past.
As an analogy, it’s like in Harry Potter, when the story starts with Harry at 11, (or, if you like, as a baby). But there is a story behind the story, and it happened over centuries.