[mothered]

Is this a correct assessment? I change my DNS to cloudfare's and when using proxy chains or a VPN, I get no DNS leak ...

If your ISP Is Intercepting/rerouting your traffic via transparent DNS proxy, thereby forcing the use of their DNS servers as opposed to the VPNs or others, then all DNS changes made on your end are futile.

It's similar to how a MITM attack works (Interception of traffic), but obviously different In nature.