I’m willing to bet the runtime overhead of assembly on the client is going to be larger than the download cost of the fragments being included server or edge side and cached
If you measure download cost in time then sure.. If you measure download cost in terms of bytes downloaded, or server costs, then nope. The cost would be smaller to cache.
Not necessarily, compression is really effective at reducing downloaded bytes
In server terms the overhead of tracking one download is going to be less that the overhead of tracking the download of the multiple components
And for client side caching to be any use then a visitor would need to view more than one page and the harsh reality is many sessions are only one page long e.g. news sites, blogs etc
