Uhm, I don't think "whatever Caliburn's prototype is" can assured taking 7 lives or more from Berserker
"The Son cannot beat the father" since the original is the purer existence, and the more one NP is modified and passed down, it's become "less pure", although its power may increased. The original is not necessarily stronger.
actually, Caliburn should be stronger since it's more famous, and the more famous, the more power a NP gain, as their power came from belief of mankind (like, Rho Aias gained its "block all projectiles" concept from belief of human, originally its only a shield with 7 layers that stopped "who that guys was called again" throwing lances, may be it had the "defensive power of a fortress" originally, but to block Lancer's throwing Lance, that only shouldn't be enough, as it's a C rank compare to B+)
BTW, I don't know what mystery/concept Caliburn carries with it, But Excalibur's concept is "A sword that can cut anything", its giant beam actually only deal damage with the tips, which is a slash, the tail is only a trail of light or something. "Promised victory" or "Assured Victory" are only the name, not the concept.
Shirou can trace stuff other than sword
But the projected results are always hollow inside
that is, until he traced a sword in F/SN
soccer ball is hollow inside, check
cloth... uhm, not really can hollow inside, check
shield, uhm, Kinoko said he can, so he can, check
But not all non mechanical items
Again, he traced spear and stuff that wasnt really sword, but they were similar, as in, they got a blade attached.
Raining of NP wont be enough to destroy Berserker 6 times if those NP are below B rank or exactly B rank
He would need at least an A+ rank (which is rare) original NP, so when he traced it, it would be B+, to take one Berserker life
there shouldn't be that many A+ NP to ensure sword rain can take out Berserker, A rank is already rare, and "rain of sword" actually is a random selection of swords from UBW, which make the chance even lower (he cant manually search and choose each sword among thousands, too time consuming in battle)
The reason UBW is E-A++ is that he can use the swords as Broken Phantasms, which raise their destruction level by a whole rank. (B rank become A rank), just like how he shot Caladbolg in UBW route