At the highest levels a conductors job is not just to get everyone to play together or to balance volumes, the better players will do that anyway.
In a professional orchestra (band/choir etc) the job of the conductor is to shape the performance. Yes by instigating subtle and almost imperceptible changes in tempo, volume, increased accents of certain notes etc the performance can sound so much better (or worse! lol).
It's also true that pro players 'up their game' when a charismatic and experienced conductor lifts the baton, a bit like when everyone is on their best behaviour at work when 'the suits' come down to see you.
All the players will be able to see the conductor over the top of their stands. You also know where the important bits of music are and you tend to look more at the conductor at those points.
Being a conductor is an amazing musical experience. Instead of just being one cog in the machine, you are driving! It's not just ego, but being in control of the whole performance is daunting and thrilling in equal measure and allows you, as a musician, to stamp your interpretation on the performance in the way that solo performers can.