yes, but this is not what you said in your original statement.

"...they hardly do anything unless you have discs or very good vbrakes." != "...a well adjusted front brake will have far more stopping power than a rear brake with the same adjustment."

the way you ride will also affect how you brake. in normal posture a front brake forces your weight forward, forcing the load of the bike and ride on the front wheel. standing up out of the saddle, putting your butt over the rear wheel, and using only the rear brake can have the same effect, since you are loading the rear wheel. on most any bike I ride, I usually only use the rear brake, and stop just fine, rarely using the front brake to scrub speed.