I understand what you mean, (I think) but from what I'm getting it only applies to FWD cars.
In a RWD car, if you understeer, (in FWD too, unless in one of your circumstances) you have lost all your control. You cannot accelerate, it will push wide. You cannot turn, your understeering. You can't really brake that well either. Atleast when the tail comes out in a RWD I still have control of (most) of my braking and steering.
Just my take on it. Correct me if you see a fault.
Sure you still have control. The difference between the understeer that Nec is describing and what you're describing is simply the initiation. Nec is probably driving his car like a racing driver, in other words, he's using the tractive capability of the car and is exceeding the tractive limit of the tires as a whole to get his understeer. Most normal drivers, and novice racing drivers, will generally feel understeer as a result of doing something that makes the front end lose it completely and totally without ever being near (relatively) the capabilities of the car, ie, early apex, early throttle, etc. This has to do with weight transfer primarily as well as other things.
Managing terminal understeer (fronts way over the limit, rears still in total passive mode, no slip angle, going to hit the wall) is just as much about anticipation as wheel spin oversteer is. The only solution is to brake. And I guarantee you have more braking force available to you than you think or what your feet tell you. A car's collective contact patch is not round, it's egg shaped. You can always use braking and throttle to exceed the car's theoretical g force limit. Say .9G sideways (maximum cornering force), maybe another .3 or .4 G forward under trail brake. I can take a Miata around an autocross course constantly playing the limit of the ABS engagement and get a really fast time. At low speeds, in a car like that, you can use maybe 80% braking pressure while cornering without locking the tires, even at the limit of sideways traction. At that speed, you need to use that much braking force to get the car to rotate into the corner.
The other thing you have to worry about with terminal understeer is what some charismatic people call "pushy-loose", which is where you have the understeer, you have a lot of lock on, you maybe lift the throttle or adjust brake pressure or pass the apex and suddenly the tires bite and the rears swing wide.
But most terminal understeer maladies can be solved by either altering line or trail braking more, usually braking more. Most people just pootle through a corner without any brake, feel the understeer in the entry and think they're at the limit. If you use the brake in the corner, you'll slowly but surely progress to a point where you can actually use the entire tractive capability of the car as a whole rather than just driving how the (front) tires tell you. This is a huge false limit. Rotation allows higher rolling speed, and allows better angle at the apex, so you can come off the corner much faster as well as get to the apex faster.
That's my interpretation of what my coaches tell me.
EDIT: Personally, I prefer and understeery car for going fast against the clock or other people, and most racing drivers of this day and age do as well. There's still people (generally with sensetive right feet and not big on trail braking) who prefer a loose car, but I don't. Sliding scrubs speed, understeer doesn't unless it's terminal (you shouldn't be racing) or just a really bad setup not utilizing the car (fire your engineer).
That said if I was buying a fun car, I don't want understeer.
