1) Other classes can do much more terrible things to your ranger and barbarian than this. Shenanigans like time stop + dimensional lock + maw of chaos + prismatic sphere don't even require feat investment, while mailman and ubercharger builds and the like can generate one-round damage totals that are likely to exceed your character's maximum hit points. Getting hit with a crit to the face is actually survivable, while those other things are not. Barbarians in particular are great big bags of hit points and can usually shrug off a critical hit if they're at full health.
2) The fact that your ranger and barbarian have no tools defend themselves beyond AC and saving throws is a testament to how poorly adapted those classes are to the 3.5 environment, not a call for the nerfing of the fighter. Rather, we should re-imagine these classes (as I've done), or provide them with new and better options (as I'm doing). For example, Combat Defense offers a miss chance, while Combat Adjustment offers an ability similar to Abrupt Jaunt that can be used to evade a melee attack. I have many more feats for melee characters in the pipeline that offer substantial and impressive defenses to match the offensive edge provided by feats like God of War