At the very first development meeting, lead developer for the set Henry Stern started the meeting with, "Can we just get rid of these?" I was also on the development and replied, "We have to at least play with them first." The Magic brand team also wanted to get rid of them
Given Valgavoth's story in Duskmourn, being the enemy of the table at large is an absolute flavor win for the story but it's easy to call something a flavor win when you don't get knocked off the table for running it
Cards that get and care about counters like Fertilid or Forgotten Ancient will help you set up the ability to use Tayam
Youre looking to cast big cards and the colourless that it generates matters
It works well in decks that want to draw a lot of cards by also doubling life-gaining effects that may buy you the time you need to actually get to play those cards
It truly drives home the idea that the spell is so dangerous that, as the flavor text implies, it had to be locked behind some tightly closed doors and the key thrown far, far away