To elaborate further, the internal names for Toedscool and Toedscruel are OKAKINGU and OKAGYARADOSU respectively (roughly meaning Land Magikarp / Gyarados).
Since the internal names haven't been updated to fit Toedscool / Toedscruel, it seems like the redesign happened late in development. Their signature ability, Mycelium Might, is the last entry in the ability index, further implying their late rework.
This is speculation on my part, but I think the main reason the Magikarp / Gyarados lookalikes got scrapped was because of Orthworm, with them likely being too similar thematically. I also think that Earth Eater (Orthworm's signature ability) was considered for both Orthworm and the Land Gyarados at first, since Earth Eater is the ability right above Mycelium Might in the ability index.