They have low drag in cruise. They have high drag in maneuver and when slow.
You don't even make any sense. What is "in maneuver" and "when slow", in aerodynamic terms? I thought you had half a century in this field and would know the right words. Do you even realize that "at high AOA", regardless of "maneuvering" or "speed", is the specific condition where a delta wing's drag really increases?
No of course you don't know such a basic aerodynamic principle, because you're also either ignorant of, or deliberately ignoring, the fact that accompanying the drag increase is a consistently high and flat lift curve that makes a delta wing planform desirable in an aircraft with a high thrust-weight ratio or a need to go FAST yet still slow down enough to land on a reasonably sized runway (concord, B-58, SR-71, etc).
This is what is so amazing about the F-18 design - the leading edge extension strakes generate vortices (and drag) at high AOA, far more so than would otherwise be generated by the rest of the wing with its relatively low leading edge sweep. The comparatively low leading edge sweep gives higher lift at lower AOA and at lower speed which permits carrier landings, yet the AOA can be spiked to previously unheard of angles in combat to permit weapons employment advantages. That takes advantage of a general characteristic of a delta wing planform, and that's why the delta wing is still used today in modified forms and configurations.
You keep blathering about how "my logic" would consider a 747 wing to be a modified delta... except that anyone with any education in the field of aerodynamics, or any real experience flying high performance aircraft with various wing shapes, can look at it and see that the basic shape is swept and anticipate likely performance properties and handling behaviors. Not only that, any investigation into the handling characteristics of a 747 (or any modern airliner) would make it clear that the wing actually behaves aerodynamically like a swept wing, not a delta wing.
Anyone with the background and experience can see and understand this, just by looking at it. Look at an F-15 wing planform and anyone with aero experience can instantly predict that the lift/drag curves and likely handling characteristics most closely resemble those of a delta wing. Knowledge of the airfoil and leading edge droop in the F-15 wing would make it even more clear that the wing's aero characteristics are generally that of a delta wing, not a traditional swept wing. A swept wing does not generally benefit from a permanent fixed leading edge droop while a delta wing does, and guess what - the leading edge of the F-15 has a fixed drooping leading edge airfoil shape.
While arguing this has been stupidly entertaining, there is one final point. By your argument, there never has been and never will be a real "delta" wing on a real aircraft, because no aircraft ever produced had a true triangle shape with a tip that ended in a geometrically precise point. They all have at least a small "clipped" wingtip due to the physical characteristics of the materials used to construct the aircraft. For that matter, simple manufacturing variations would ensure that the trailing edge of the wing is never precisely 90 degrees from the aircraft's centerline. There will always be a variation, hence by your definition, there will never be a true delta winged aircraft.
You can't even get the basic aero terminology right, your overly narrow definition of a "delta" wing is physically impossible to manufacture, and you are ignoring the fact that the aerodynamic properties inherent in a "delta" wing are the product of airflow over a wing planform that is roughly a right triangle but not necessarily a precisely true or simple right triangle.
