While this statement is correct, it doesn't apply to the lowest levels. the actual reduction in the numerical value of stamina is negligible to zero. If your health currently is at least twice your base health, your health should increase noticeably.
e.g. your base health is 800 right now and your total health is 2k. In wod, your 120 stam becomes 2400 health, plus a very small base stam (estimate 200 health maybe?) or a total of 2600, higher than the 2k you currently have.
If you have great stam and 2400 health now, the same math applies and you now have 3400 health. So, the better you become geared as a twink, the larger departure from your current health pool will have.
Now, that aside, numbers aren't final and we'll need live beta testing before conclusions can bedrawn.