My understanding is that beats in music are well defined. Imagine a pianist hitting 3 notes to the bar (as if playing a waltz tune)from the written music. the first beat starts at the instant he hits the first note, and continues until he hits the second note. The resulting sudden increases in sound level as each note is struck are universally identified as the 'beats' in the music. 1& is the moment in time halfway between striking note 1 and striking note 2(for the simple 3 notes-to-the-bar music).
How a condustor behaves is up to the conductor. They all have their own methods

I concur that beats are well defined. Each beat has a beginning point and end point. It's clearly distinct or should be if the band is to stay together. How each instrument produces that beat is a different matter. A string instrument vs. a horn instrument vs. a percussion instrument...each initiates the production of a beat at different times (because of the time differences it takes to resonate a sound), but the beat(or the sound) has to occur (or be heard) at the same time. The tempo is, however, subject to the conductor's desire and all instruments should adopt the tempo he sets.

guestAt. Whilst we are into the music and beat values and so on there are other things to taken into consideration. First the Tempo is set to the recomended spead. More about that in a minute.
The way we fit our steps into that music is another thing. In recent months I am being taught to stay on the supporting leg longer. So instead of my right leg drawing level with my left. I hold it in a position behind staying there untill the tip of my toe only is on the floor. Then moving it alongside my other foot. This causes an alteration to the front leg in so much as I need to have at the excent of my stride two straight legs. The heel of the front foot on the floor and the toe of the rear foot on the floor. A simple test will more than likely show that most front knees are bent too early. That's if they were straight in the first place. The front knee should start to flex only as the weight is sent forward from the rear foot. If you watch your videos you will get a clean view of that back foot. The lady will be matching this but going backward. It would be worthwhile looking at the pictures in the Learning Centre.
Tempo. In the days when there was little in the way of controlling the speed a record was played at. We relied on the recording and the orchestra. Being that some were recorded slower than others we finished with an official recomended tempo of for the Waltz 31 Bars per minute. (BPM). Rumba was 28 to 31. I don't think anyone dances a Waltz at 31 any more, and the Rumba is down to about 25 BPM. My complaint is that if a music presenter puts a Rumba on at 31 there could be no complaint. But those who have been training at a slower tempo would be at a disadvantage. I believe every year there should be a review of the Tempos and they should in a competition be played only at that speed and not at the discression of the music presenter who possibly can't dance. We have a style of dancing which are competition dances. Would you believe the recomended tempo is between 48 to 52. on one dance. That is a big difference especially if you have been training at 48 BPM