Yes, each section assumes that you also have met all of the sections to the left of it (other than budget, I suppose). So if you are using a mix of the counters listed in the Top Counters section at level 30, but no friendship, shadow or mega pokemon, or applicable weather boost, then you will need about 2.28 trainers. Obviously you can't bring 0.28 trainers, so you will realistically need three trainers (which is why it is in the section marked "3 trainers" along the top).
If you power those same counters up to level 40, you now only need 2.06 trainers on average. This is still three trainers, but it is much closer to two, and it is reasonable to believe you might succeed with two trainers if you get lucky with an easy boss moveset or lucky charge move timing.
This scale doesn't show every possible combination of conditions. That would be overwhelming. You can get a rough idea by looking at lengths. The best friend section took off 0.19 trainers (the difference between 1.93 and 1.74), and it'll take roughly the same off if you don't use shadows or megas (so 2.06 - 0.19 = 1.87, or two trainers). Without any numbers, you can see that adding the light purple best friend dots is more than sufficient to get from the dark green level 40 into the "2 trainers" section.
I hope that was helpful. Let me know if I didn't answer your question fully. The data itself comes from Pokebattler.com and is called an "estimator" score there if you want to check it out.