IT's not clear to me from this article why exactly a Big sur update needs 600MB of firmware updates and ???GB of dynamic linked libraries. I must confess to not

IT's not clear to me from this article why exactly a Big sur update needs 600MB of firmware updates and ???GB of dynamic linked libraries. I must confess to not really knowing the design and consequences of Big Sur's sealed system. This article could really use an overview like that. I'm going to go out on a limb and speculate that all updates need to be signed and this makes sure that every Mac gets the same update and uses the part it needs. I guess the alternative is a combinatorial explosion of different combinations of firmware and hardware. But... there's not THAT many Macs (even years old ones) so I'm a little confused. Does this SSV system actually improve security or is it just security theater (serious question)?