“Their project involved primarily the facade, where many of the statues over the portals had been beheaded or smashed during the Revolution. They proposed two major changes to the interior: rebuilding two of the bays to their original medieval height of four stories, and removing the marble neoclassical structures and decoration which had been added to the choir during the reign of Louis XIV [. . .] Instead, he proposed to rebuild the original medieval spire and bell tower over the transept, which had been removed in 1786 because it was unstable in the wind.”
If you want to restore the original style then we should remove the gargoyles, as mentioned, but also other elements that were added.
Even the spire was not a 'replica' as it was taller than the original.
There is no point seeking to restore "as it originally was" for an 800 years old building.
Certainly not using any lead anymore would be welcome. it's also debatable whether timber should be used at all as it's not even visible to anyone.
There's another very old building in Paris that was recently refurbished (collège des Bernardins). They remade the roof using steel and titanium tiles. It's lighter, does not burn, and will last centuries without any problem.
Bolting on visible concrete, steel, transparent glass is a clear discontinuity from the medieval design.
Classic 'this concept cannot be 100% unambiguously defined, therefore it is entirely meaningless and anything goes' argument.
There are no definite boundaries between colors - they blend into each other continuously, and there is never a sharp transition as you move from white to beige to red to blue in color-space. So why not paint your office and house, inside and out, bright red? After all, the current color has all sorts of pigments, so you can't really say the 'original' color wasn't retained!
Notre Dame was refurbished and changed in the 19th century (and at various other times) . For example, the famous gargoyles are not 'original' at all but date from that time.