The TGV does not, and cannot operate through the Channel Tunnel, due to voltage issues.
But there are versions of the TGV, Thalys, which operate on three or even four different voltages.
For services through the Channel Tunnel to be viable, they have to be able to buy the track paths, and this is easier to pay for when you have 400m long trains,
So why have DB applied for permission to operate trains considerably shorter than 400m through the Tunnel?
I also don't agree with the proposal, but when arguing against it, you need to get your facts right!