As a normal, pretty casual player i finished meta achievement within a week with relative ease, without any of the strike mission achievements, i think your math is wrong, OP.
You're probably balancing the damage from boss around players who run full glass builds. Because even if you have a bit of toughness and vitality and facetank every mechanic its just tickles your hp bar slightly. I'd say all damage numbers should go up by 100-200%.