Carousel and long-line layouts get compared on throughput, which is the wrong axis. Both can be fast. What separates them is how much the product changes between pours.
A carousel earns its cost when the product mix is wide and the cycle is short. Pallets circulate through fixed stations, so changing what is on the pallet is cheap. Changing the stations is not.
A long-line bed is the opposite. Setting up costs a shift; running the same section for a week costs almost nothing. For hollowcore, piles and bridge girders it is hard to beat.
The failure mode in both directions is familiar. A carousel bought for a single high-volume product spends its life underused. A long-line bed asked to serve a wide product mix spends its life in setup.
Before specifying either, count how many distinct sections the plant poured last year and how many times it changed between them. That number decides the layout.