DPS parsers are a good indicator to measure differences between players performance for damage.
They usually don't take healing and tanking into account directly.
Though a tanking/healing ship has a better chance of staying in combat longer.
A dead DPS dealer will diminish his overall DPS by not firing any weapons for a while.
And then the parsers only take into account actually dealt damage.
They don't measure the raw output I think which can be diminished significantly by resists and defenses.