I've always considered Poison to be a significant part of pokemon's mechanical identity. A battle system that lets status flourish compared to a lot of other RPGs giving bosses blanket immunities. An entire type devoted to the concept, and a common type during the early games at that. A poison move being universal was a part of that: it let every mon have meaningful access to this part of the game. The lack of replacement for Toxic and the shift away from trainer bosses are what flips my internal perceptions from "these are pokemon games with little enticing content" to "these are no longer pokemon games as I understand them."
At some level, I wish I could stand to play in formats with the moveset retoolings. I can agree that Knock Off was overbearing and that Chilling Water was a good fix for some of the problems with Scald. But it doesn't feel right without Toxic. Even in Natdex, where older mons lose nothing, its absence is a serious damper on using a major chunk of new mons. Have a lesser replacement if you need to, I'll point again to Chilling Water. But I need there to be a universal damage-over-time move.
