Don't be naive.
200mm f/2 - 70-200 f/2.8
300mm f/2.8 - 70-200 f/2.8 + 1.4 TC
400mm f/4 DO / 200-400 f/4 - 100-400 4.5-5.6
400mm 2.8 and upwards have no zoom equivalents in the range.
A stop is a lot. Don't belittle that fact.
Except for the 400s, those aren't supertelephotos. And the 200-400 doesn't officially exist yet.
Your original quote specified "super-teles" versus "L-grade zooms"
Check the EF Lens lineup here:
You could maybe make a marginal case for your original point by comparing the 400 f/5.6 against the 100-400, but the 400 f/5.6 is really just a 300 f/4 with a built-in teleconverter. Generally, "supertelephoto" really only applies to lenses with a physical aperture of 120mm and bigger.
But your original statement, that it's only one stop that separates supertelephotos from L zooms, is quite misleading. Those zooms all have apertures of about 70 mm. Indeed, that's almost a constant from the 70-200 f/2.8 all the way through the 100-400, as well as the 300 f/4 and 400 f/5.6 primes, and even the 85 f/1.2. In contrast, the majority of the supertelephotos have apertures twice that size, which is why they're in a league all unto themselves.
One stop of light is the same difference between the 135L and 100L. Which is the same one stop which seperates a 70-200L to a 200 f/2. Some are willing to pay the 5000$ for a stop yet, you belittle the twice the light advantage of the 135L as not a reason to chose it over the 100L. Super tele, meh, I use that term loosely for big expensive glass that 99% of people won't own.
The principle is still there in my comment, a stop is big step and enough to choose between lenses.