Perhaps I'm missing something, but unless you use your floor jack to lift the car entirely off the ground, you only need your jack to support the part of the car you are lifting.
In round numbers, lifting the front of our 5000lb car is 2500lbs of load, or 1.25 ton. The remainder of the car's weight continue to be supported by the opposite axle. That's well within a 2 ton jack's nameplate rating, to say nothing of a 2 or 3 to 1 safety factor they are likely to have designed in.
A bigger jack is safer, of course, and probably more stable (ie, bigger) but with that comes a higher weight and cost.
Regardless of the rating, any jack can fail. Always use a jack stand as a backup. Don't ever go under a car without a safety device of some kind.