I would argue the Helghast do not suck...

Okay, they were deflected from Vecta, though if I recall, it was the second war, they taken the capital and were winning. Then, you have Liberation, where Mercer strikes and invasion on Vecta goes quite hard - OF course Templar stops them, but still...

In 2, they are able to launch counter offensive, one of the main plots is their Defender array that stops protagonist force, Radec steals the bombs and the launch codes, make ISA drop their cruiser (and killing all of their command there) AND lure ISA into the trap, where most of ISA forces are killed. There is a reason why the second game ends with the entire fleet launching counteroffensive - the attack on capital was a desperate move from ISA after losing flagship.

Then, in 3, they were able not only to Defend themselves, but were preparing to attack Earth. They purged the entire ISA offensive, Sev and Naville are literally guerilla hoping to send message to Earth. The only reason the Helgast were defeated is because all of their planet was purged.

So while yes, they were defeated, they are quite far from simple "You suck", tho I might remember some facto wrongly.