Well, I suppose it's a matter of perception. I'm not saying what happens in "high level play" (I prefer "team play") is the be-all end-all but by the same token it'd be a grievous error to balance the game around the common denominator. I mean when you see a snoozer who's using Sci Team for main healing, triple photon torps and none of his Captain powers, his problem is far more fundamental than how he's managing his Defense score.
I guess it'd be one thing if snoozers/Sci tubs couldn't keep themselves safe because their Defense was tanking in organized play, but that just really isn't the case; team play can only extrapolate from the game's basics that apply anywhere but that doesn't mean everything just becomes harder, faster, stronger once you leave pug land. Hell, the most brutally unkillable fortress of a ship in the game (Recluse) has a terrible Defense capacity and it's super vulnerable to holds and CC. It just tanks it all anyway and throws it back because it has such an ungodly shield/hull setup. A well-built Ody isn't quite as monstrous but it's damn close at times.
Say that you're a snoozer getting t-beamed by an escort. There's a great sequence of steps that'll keep you fine and dandy so long as you're quick on the buttons (this is less for Thissler and more for readers):
1. Is Tac Team up? If not, wait for the 'scort's very first offensive buff and hit it or call for a copy (you can keybind this if you're strictly pugging);
2. Hit EPtS and TSS and switch to a 25/75/25/75 setting. As he ramps up the heat, hit more resists in turn, along with a shield battery. If he goes full beast mode with all guns roaring, hit Scattering Field/Sci Fleet or RSF/Eng Fleet and another TT. If all else fails, hit RSP and manually distro (in all honesty you'll rarely need to hit RSP, use it as a last resort).
3. His major offensive buffs have now worn out and he's a meek little kitten, while your powerful resists are still respectably chiming off of CD.
In all of that, you'll notice there's no need for a hold immunity. It's because on a snoozer your Defense score just isn't worth speccing into; you don't need it, and the powers useful for speed tanking (PH, AP:O) don't have good team synergy.
It's true that I said Defense is a poor stat to base your ship around. However, this is why 'scorts and tiny ships are far more dependent on their healers than healers are on their escorts: snoozers just don't need Defense to keep themselves breathing, while 'scorts need everything they can get to make the most out of their measly EPtS1 and stuff.