This really reflects a change in the culture of gearing in the game.
There has never been a time in the entire history of the game where a step higher in content remotely required having every single slot occupied by something from the previous level of content.
In reality, if raids are tuned anything like they have always been traditionally, being around 456-457 should be plenty of gear to start normal mode raiding, much less LFR.
LFR is catered to a hyper-casual completionist gotta-catch-em-all culture of gearing, where you're a failure if you don't have the highest ilvl in every slot. This is different than the culture of normal/heroic mode raiding, where you are trying to attain the maximum success as far as possible in the minimum gear by intelligent strat choices, class synergies, min/maxing what you have, etc.
In other words, the 463 requirement is not so much anything to do with the difficulty level of the game itself, it's to do with the fact that the hypercasual gear collector demo that LFR is made for need arbitrary stupid rules like that, because that's the game that they're playing.