Your calculation for takt are absolutely right taking an average demand is the wrong part. We take maybe a six month look ahead in orders that is the customer demand. Takt may change up to 8 times a year on some value streams.
In aerospace we had 9 different aircraft types one would be on a move rate of three a week some one a month each had an individual takt time based on the demand for that product.
The cycle time of each key stage or process was then evaluated if it was greater than takt you had to in goldratt terms exploit the constraint. You would create a yamazumi or line balance chart to identify the constrained stages from seeing this you can do many things .
Identify Value and Non Value add. eliminate the waste to get below takt. Introduce shifts on some stages or create identical stages called rate tooling. So you never under or overproduce as you are asking because the speed of your line increases and decreases with customer demand by flexing tooling positions and manpower.
Usually you had the luxury of one value stream getting faster as another slows down moving your manpower onto different contracts.
Hope you get this
All The Best
If cycle times vary widely, whether from cycle to cycle, or from person to person, it is an indication that there is something wrong with the process. On occasion, you will have one person who can’t seem to keep up. Make sure you observe the operator before you to jump to conclusions. In all likelihood, the person is slower because he is not following the process, not because he can’t do the work. In most cases, this is a training problem, meaning the operator doesn’t know the right way. That’s not the operator’s fault. It’s yours.