Doing Waterfall correctly is easy. Spend 1 year planning, 3-5 years building, 1 year testing, then release. Find out you built the wrong thing, enjoy the earnings from your $10 billion government contract, and start another cycle.
I think that "waterfall" is often a straw man.
Every discussion where Waterfall comes up has someone saying this, I'm glad you've not experienced it. But it has existed, does exist, and will continue to exist (because enough project managers are idiots). One of my first jobs (I quit) was a failed project that persisted because of gov't money, but would have failed as a commercial venture (started circa 2007, failed to deliver at least through 2011, I was on board for a year and found an exit). It was 100% Waterfall, they literally delivered the wrong thing several years late and with around $1 billion spent. Great for the contractors, awful for the taxpayers.
But yes, that is what Waterfall is. It's a large scale project executed linearly with limited-to-no-feedback. Large scale is somewhat subjective, but basically if it's done in less than a few months it's probably not at a scale where your choice of development model actually matters.
Estimates are never accurate. You can’t possibly have all of the information present up front.
Waterfall's principle failing for large scale projects is that it does not incorporate sufficient (if any) feedback or delays the feedback until too late in the cycle, and plans too far out to be reasonable (do you kwon with any real confidence what you'll have for dinner in 3 years, 2 months and a day?) V-model generally also plans out very far, but incorporates V&V as an ongoing activity (it's name is a bit of a pun, both incorporating V&V and usually being charted out as a V, vice a waterfall for Waterfall). I&I may have a big design phase, but it's usually not as fully designed as either Waterfall or the V-model because the iterations are meant to provide checkpoints for validating the design and potentially changing direction (like I wrote, slow-motion Scrum).
If the company from top to bottom isn’t Agile then I don’t believe you can truly be Agile.