So what's the difference between 1/4 and 1/2? In either case, we're talking about a huge portion of monsters a person will face in hell difficulty being immune to your primary attack. That's just bad. Fire blast and death sentry are both unreliable and, while they might rescue you from one or two easy targets (lightning spires in the arcane sanctuary come to mind, in the case of fire blast) they really won't save you at all from major situations. Without some pre-slaughtered corpses, Death Sentry is going to do nothing but spit lightning at your LI targets. And fire blast is weak to begin with, it's slow, it's pathetic for area damage. If you have the time and patience to wrangle a bunch of enemies into a little wad then chuck some fire blasts in the middle, go to it ... I'll stick with an assassin that can handle immunes of any sort.
As for shadow masters being reliable sources of damage ... I have to disagree. Building my most recent assassin, my shadow master walked pretty much all the way through each act of hell right beside my character. Maybe she doesn't hit as hard as I do, but she definitely pulls her weight. Not only does she melee very capably, she will cast things that I haven't bothered to learn, which is super-helpful. Diversity, you know?
As for hybrids being difficult ... maybe you can't walk through the game never seeing the majority of your enemies, but you won't get caught begging for help or breaking yourself trying to kill a dozen monsters with a skill you only know 'cause it's a prerequisite to your real skills. Nobody said hell was supposed to be easy, either. What's the fun in all that?
The simple fact is, you'll run into this problem no matter what you do if you're too focused with your build. Sorceresses that use any less than three different elemental weapon skills run into walls. And you can't always just teleport away, either. When they released the new patch, I went hunting for keys with my meteorb sorc. Didn't take too long to realize that there was no way this character could ever, ever possibly kill the Countess. Not if she's going to come up as Fire immune and Cold immune every time I play. For better or for worse, the same goes for assassins. Trappers can do a lot of things really well -- they're great for PvP if you know what you're doing, and you can MF with them easily too, since none of the act bosses are actually immune to anything. But if you're going to play through the game -- especially solo -- relying on the traps tree will get you a whole lot of damage and a whole lot of enemies who are immune to everything you've got.
You're right, though, Tiger Strike and Dragon Talon is a bad combo -- I meant to say Tiger Strike and Dragon Claw, or (as an alternative to both) kicking, which would be: Dragon Talon.
Seriously though, some of your comments lead me to think you haven't played a trapper in 1.1 or 1.11. I don't know of a better guide than JRich's that the first post mentioned. Try it. Try it without the enigmas, ctas, sojs you mentioned earlier. Even try it untwinked and hc. And then come back and tell us how weak trappers are.