I have watched and also listened to the music you have all posted.
My question is this?
Do any of those musicians actually look at the guy prancing his arms around like a fairy? Is sure doesn't look like they do...
Although musicians may disagree, my experience suggests that the conductor's hardest work is often unseen. Generally, at rehearsals, he (or she) will go through the music and decide on tempo and other specific parts, often in great detail. By the time of the performance, then, professional orchestras will already be familiar with the way the conductor wants a piece played and will therefore not need to keep glancing up to be aware of the tempo. That said, the conductor can still use signals to emphasise or remind players of certain requirements. A conductor can make or break a piece. One of my favourite pieces is the St Paul's Suite (Holst). I have it on CD, recorded by the RPO. However, Classic FM always plays the piece recorded by another orchestra which is played at a much faster tempo and, to my mind, the music is spoiled. I don't know which is definitively correct (though I could guess), but the change in tempo is purely down to the conductor alone.
I would emphasise, though, that I am not a musician...these are just my thoughts.