Utterly invalid point that assumes aircraft development is linear. These planes have been around for a long time for good reason.
Operationally, the KC-46 will be more or less identical to the KC-135. It will carry marginally more gas, burn a bit less, and be able to get a little closer to a threat. All for the low price of $250m each. The KC-135 has been around so long because it works fine. A tanker doesn't need to be cosmic.
The U-2 argument is shit because they were redesigned and built new in the 80s. The S-model today has a F-118, the cockpit is all glass, and the sensors are the illest shit around. The "newer" HAISR platform that the USAF spent the taxpayer's hard-earned money on is inferior in nearly every measurable category.
The Buff can still end the world at a moment's notice better than it ever could, so there's never been much incentive to get new ones. Even after we buy $60B worth of LRS-Bs, we're still keeping the Buffs anyway. Did the chief mention that part?
Edit: TLDR: The B-17 was inferior within 10 years of its first flight. The 3 aircraft above are still relevant and their replacements will either be similar in capes, a newer version of the same design, or not even required.