Follower count in Helix /streams endpoint?

Nope, you have to go call the followers endpoint

It’s a toss up, since not all “users” are “streamers” and thus won’t have “followers” so would seem they dropped it for performance reasons.

So you can fetch and cache it yourself instead.

Or consider making a suggestion to Twitch

https://twitch.uservoice.com/forums/310213-developers