What is the difference between using a HWW with a full node and using a full node to verify the balance on them?

I started my bitcoin journey by getting a ledger, then I got a trezor, and only then did I start running a full node. Since I used both those HWWs without a full node before, my tx data was already sent to their databases (or their nodes at least).

Right now I'm struggling to get my node to behave with Specter Desktop, so it begs the question - if my xpubs are already stored in Ledger's and Trezor's databases from using their HWWs without a full node before, what is the difference between using a full node with those HWWs through Specter Desktop, and just continuing to use Ledger Live or Trezor Web as the interface to my HWWs but then verify my balances and transactions on my full node?

Furthermore, how can I update the firmware of my devices without using Ledger Live or Trezor's web interface? Is there a way to do it that doesn't leak your xpubs?