Lol, shield isn't useless, it is actually overpowered. When you have 100+ resistances, physical attacks are only way to kill you. And if you don't have leech + comeback kid, nearly 100% chance to block is perfect way to prevent that.
the thing is people should not be immortal.
even if these things did not exist, its fairly easy to exploit the invisibility and sneak mechanics to completely avoid enemy retaliation. if you end each turn invis or sneaked they just stand there and let you kill them.
however, this is not what i consider good gameplay. if my characters become immortal through resists/shields or exploiting an invisibility tactic then i am just going through the motions. there is no challenge or sense of accomplishment.
resists and block should be capped off at a reasonable level so you still take some amount of damage and if the entire team is invis/sneak then enemies should use AOE effects randomly to see if they can hit you.
things like that would at least keep some amount of involvement in the combat.
as it stands by mid levels with some decent planning combat devolves into a derp-fest of shooting fish in a barrel using dynamite.