Ditto being a failed Mew clone is the only theory fans discovered that is obviously true. Every video game that has ever existed has content cut before its commercial release. Masuda or whoever denouncing the Ditto-Mew theory doesn't mean anything. Of course a dev would denounce remnants of an alpha version that wasn't intended to be in the final release.

There is an entire website containing content cut from games: https://tcrf.net/Pok%C3%A9mon_Red_and_Blue

Aspects that prove the relation between Ditto and Mew include the following:

- Uniform Base Stats. To this day, all 6 Base Stats being identical is EXCLUSIVE to Mythical Pokemon (e.g. Mew) - with a handful of outliers like Sunkern, Castform, and DITTO. This trend has been the same for 30 years, so it's clearly intentional, and Ditto does NOT fall into this VERY exclusive group by coincidence, as you will see below.
-Ditto and Mew have the EXACT same color palette in both Normal AND Shiny form. As an artist I want to emphasize they use the EXACT same shade of pink for the Normal form, and the EXACT same shade of blue for the Shiny form. It's not "One has a sky blue Shiny, and the other has a cerulean-colored Shiny". It's the EXACT same shade of blue for BOTH in BOTH FORMS. This is NOT a coincidence, and Masuda or whoever denouncing the theory with evidence this obvious is an insult to the fans' intelligence.