You know that fallout 3 mod that made power armor useful? Impervious Power Armor...look it up on the Fo3 Nexus and try it out, it added a kind of extra script for damage resistance on the power armor, depending on how high the DR of the armor is(I.E, T-51d is 40, gives you invulnerability against anything doing 10 or less damage, stacks in some way I don't understand), will dictate how "invincible" you are, instead of being just some tin-foil soldier waiting to be one-hit by a deathclaw or taken down in seconds by a few super mutants with assault rifles.