Because the copy is finished before release, yes. Classic has all the characters, and there's no delay for copying when you select Classic. TBC can cause delays, simply because it's not instant. It can also result in WOW TBC Classic Gold a lot more characters being copied simultaneously. This could lead to the system going down.
The boost mostly becomes a problem as botters will most likely use it, which can cause more of an issue with bots. But if bots were removed, I don't think the boost would be any issue. I have 5 friends that are coming back to buy WOW Burning Crusade Classic Gold classic because we all like tbc, and they only join due to the fact that they can increase their levels beyond the vanilla content.