DPS is, by definition, a "sustained" parameter that can easily be a rather poor indicator of actual combat performance.
Maybe not quite so poor on direct-fire beams, but there are several weapon types for which a DPS stat is a weak indicator of usefulness. Fighter cannons (outside of strafing runs), dogfighting missiles, slash beams (at any sort of range), and slow-charge beams (like the SGreen) would have poor damage over time but impressive "burst" damage.
Cliche of the day: you've got lies, damned lies, and statistics. Numbers are numbers, it takes a little thinking to parse them properly.
Really DPS should be removed from the infobox entirely, DPS (sustained) should be renamed to DPS, and firing time should be added so you can still calculate the old DPS parameter if you for some reason want to.
I agree with this on principle, but I see why the current "DPS" number exists: as an already-converted value of the beam's $damage entry. That said, I think the current "DPS" value isn't particularly useful. Per-pulse and long-term "sustained" DPS values are far more valuable.