Pretty sure like 4% of Vanilla players played Feral. It wasn’t overly popular.
Can’t find that stat, but I remember a Dev saying it at one point. I did find this though, https://www.wowhead.com/classic/news/classic-wow-realm-population-report-data-aggregated-through-community-295075#class-distribution
Druids have always been a high-skill cap but low-reward class in Classic. You had to put in a ton of work to be as successful as an auto-attacking warrior pressing keys at random. You could be more successful with another class doing half the work. TBC is when druids REALLY picked up.