Sun just obliterates anything, there's really no solid counterplay to sleep powder + Set Up on mons like Bellsprout and Bulbasaur, and while there are niche checks like Scarf Trace Porygon, having to resort to such abnormalities is a sign of unhealthy presence. Vulpix just made setting 8 turns of sun multiple times in a game too easy and allowed for Chloro sweepers to run rampant on almost any team far too easily.