That’s sort of depressing. I’m sure I don’t fully understand, but does this mean anyone using QT as their wallet is leaking info about their transactions,
No, Bitcoin Core synchronization is fully private.
or this is limited to “light clients” which Sparrow acts as on top of your node?
It's a specific issue with Sparrow's light client. Other light wallets like Wasabi, Bitcoin-Safe, Zeus, Blixt, and Breez protect your privacy during synchronization by using BIP157/BIP158 compact block filters.
Are old full node wallets actually more private than Sparrow by default?
Almost every other wallet is more private than Sparrow by default.
Lastly, does a VPN or Tor help at all? You can still see the btc addresses but not linked to IP address? Thanks for the heads up
Tor is a nice privacy improvement, satoshi thought so himself:
https://bitcointalk.org/index.php?topic=7.msg66987822Wasabi uses a unique Tor IP for every tx broadcast, peer connection, and coinjoin registration by default. No configuration required.