Well with your DVDs the “HD resolution” question is easily answered: you don’t get HD resolution. Weird comparison there. Especially since you complain about Disney+ not going beyond 480p in your specific case - so why buy DVDs with the same shitty resolution?
While I generally agree here, resolution isn’t everything, bitrate also plays a role, and some content in streaming services has been compressed rather badly so that you get artifacts that you don’t have on DVDs. A DVD will certainly look better than 480p streaming content despite a much older codec which light only exists as a reason for an upsell.
I think the way to go is a Homeserver (could even be a raspberry pi) where you can somewhat secure your storage with appropriate redundancy.
And how would you get stuff onto your homeserver legally?
I mean if you’re going for the piracy route, you never used streaming services or bought physical media anyways and the whole discussion is moot.