I once had an ISP which did transparent http proxying. You could theoretically query an external DNS server and get back the correct result, but it would intercept your http connection, discard the ip address you were trying to connect to then do a new DNS lookup to the ISP's DNS server on the HOST header.
Took me ages to work out what was going on with the various issues it was causing.
I dumped that ISP like a rock after they refused to disable that caching proxy, which they claimed was only there to improve customer experience.
However, if have a local TLS nameserver, you can set it up to query 1.1.1.1 over TLS, then your ISP can't see any of your DNS queries.
So you need to decide who you trust more -- your ISP or a DNS provider (or a VPN provider).
But these are different people, with different incentives. The NS owner may be logging everything, without the domain owner's knowledge, and the NS owner won't even be in the wrong, because they likely made no promise to not log.
With a single resolver, I can verify that they're trustworthy enough [for me], just once, and direct all my traffic to it. Cloudflare's "We committed to never writing the querying IP addresses to disk and wiping all logs within 24 hours" is something, I imagine, they very much wouldn't want to be caught violating or changing their mind about later.
In the meanwhile, with the root NS method, I can only hope that my queries will get lost in the "noise". And I'm putting noise in quotation marks because there isn't much diversity in the name server ownership: 75% of Alexa top 1M domains are hosted at Cloudflare, GoDaddy and Amazon. [0]
[0] https://www.datanyze.com/market-share/dns/Alexa%20top%201M/
QNAME minimalisation will only send <randomstring>.com to the root for them to give you the referral.
and RFC7129/RFC8020 mean that when you get a NXDOMAIN back from the root, you'll cache it and never try again for a large swath of possible names.
Apply this deceptively simple principle to every need you have on our wonderfully decentralized Internet and see where that gets us.
Oh snap. Not so decentralized anymore.
Okay, say, 1 year from now, somehow, 95% of internet users are sending their DNS queries to Cloudflare. What can go wrong? Malicious or not. Not rhetorical, actually curious.
Centralizing things, makes it easy for law-makers to enforce bad policy which technology otherwise would have side-stepped.
If your local DNS server is merely querying an upstream resolver (like 1.1.1.1 / 8.8.8.8) on your behalf, then yes - it is no different.
If however, you query the root nameservers for the glue record for a domain and query the domain's own nameservers directly, then it is pretty good... As you are neither querying your ISP or TheMan.. which means that logically only the domain nameserver owner knows what queries you made (and you are probably hitting that domain in a moment anyway!). (The caveat is that some ISP's do transparent DNS proxying.. in which case, you have much larger trust issues with your ISP and need to take greater measures!)
That said.. I cba with that.