Super Mario, Yoshi, And The Hardware Limitation Claim

While playing Super Mario World before - I was thinking about the bootleg by Hummer Team and the Nintendo official game. There was the claim that Yoshi himself couldn't be introduced due to hardware limitations. I don't know if it's even a valid claim considering that Super Mario World the bootleg edition had Yoshi after all - except that there was only ONE KIND of Yoshi. 

One game worth mentioning is Adventure Island 2 and Adventure Island 3. Consider that the protagonist Master Higgins rode four different kinds of dinosaurs each with a different function. Okay, none of them ate the enemies but still, you can't deny that he rode the dinosaur, right? The bootleg Super Mario World had Yoshi eat up enemies. So, what could be the much bigger reason behind Yoshi's non-introduction?

If the claims for hardware limitation are true then here's my theory. Super Mario Bros. 3 invested too much in different suits making it impossible. If the game itself didn't get different kinds of suits that went beyond the mushroom and fire suit - Yoshi could've been possible. But no, I think focusing on the suits made Yoshi impossible due to hardware limitations. I think Nintendo could've further elaborated by saying that their emphasis on this didn't give space for Yoshi. Not to mention, the graphics of Adventure Island 2 and 3 are inferior to that of Super Mario Bros. 3. I guess the claim must be real if you judge the quality of graphics between games, right?

Though, I think they could've actually said Super Mario World is where it all gets together. The official game can't fit into the NES cartridge plus it was going to be a very ambitious game. I think they simply knew it was time to move on to the Super NES since they had twice the ambition. The NES is 8-bit but the Super NES is 16-bit.

What do you think?