First of all, LOTR didn’t replace all actors in any battle scene. They used their brand new ‘MASSIVE’ software for the tens of thousands of characters too distant to distinguish from the hundreds and thousands real actors used that were visible.
The other difference is that scale - it was literally not possible for LOTR to have enough extras due to complexity, local population, and budget. This is a scene with only a couple dozen people on screen at any moment.
First of all, LOTR didn’t replace all actors in any battle scene. They used their brand new ‘MASSIVE’ software for the tens of thousands of characters too distant to distinguish from the hundreds and thousands real actors used that were visible.
The other difference is that scale - it was literally not possible for LOTR to have enough extras due to complexity, local population, and budget. This is a scene with only a couple dozen people on screen at any moment.