These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Fridge Brilliance/Wild Mass Guessing: It's not taken seriously. Allo knew that Rex as a largely Harmless Villain, but on Reptilon he probably was far more of a nuisance. If he managed to get the idea of fighting on Earth into Rex's head, where he'd have to do so in secret, he became even less of a menace. Allo's basically just wasting Rex's time and keeping him out of any real trouble.
There was some hint that it was Princess Dei that was involved with putting the idea into Rex's head, to get him and his entire looney crew out of her...hair. The Dinosorceror and Dinosorceress subsequently sent Allo and the gang to keep the Tyrannos out of trouble and from doing too much damage, and conveniently, it got the entire bizarre lot of them out of the Sorcerers'...hair.
The Scrappy: Making no claims about how wide-spread this viewpoint was, some Dinosaucers fans hated all the human characters equally, for taking up plot and episode time that could've been devoted to the dinosaurs.