I only tested it with lone wolf on Hard, but I would say that it is allways worth it. And that is because vitality is not reduced by 50% at all. Only base vitality is reduced, and vitality from gear is not reduced at all.
I had 2 lone wolf both with 10 in constitution and both with 6 base points and 4 from gear.
The one with glass cannon had 1158 in vitality ond the one without had 1642. That is only 30% reduction in vitality, but twice as many recovery AP. (That was on normal before I changed to Hard)
Don't put points in to constitution, put them in other attributes and focus on getting constitution from gear.
And of cause the difference in health between glass cannon and not will become smaller the higher level you get to because you will find more gear with higher constitution additions +2.
In some fights with many enemies you might need to put out a decoy (spider) to soak up attacks until you get your high recovery AP's and can thin out their ranks. But I would say that glass cannon is allways a given (you might wait until level 11, so you have collected enough gear with constitution points, before you select it if you want it easier).
