router99 I don't think that's a good way to put it. If the traffic is routed to a VPN server, that's the only destination they see and nothing else.
Wrong. Very wrong.
Even if you use a VPN, your ISP will see 1) how large the file you download or upload is, and file sizes alone is often enough to know what file it is, 2) the exact point in time the upload or download was made, which might be correlated to when a peer or file appears in a swarm or on a site, 3) the speed at which you transferred the file, including ups and downs, this is something ISPs log at 5 second resolution and that can be used to correlate your activity, even years later, 4) when you send small amounts of data, which if they have enough samples can be used to correlate with when a certain anonymous online identity makes public posts, thus deanonymizing you, 5) when you receive small amounts of data, which can be correlated with log entries in server logs.
And this is only the passive attacks your ISP can do. Here comes the scary active one: Your ISP can cooperate with the exit node or destination server to introduce specific patterns in your transfer data, such as changing upload and download speed, to completely correlate and deanonymize your connection. This is the one that is the reason everyone says the first hop must be as trusted as possible, to minimize the risk an attacker is in a position where they can monitor your entry into the network.