Collectors are undiluted idiocy and anyone who defends them deserves nothing but mockery. On Gold and up, they do more damage and are harder to kill than literally every other faction. The Collector Captain does huge damage - more than any other non-boss unit - which increases to higher than a Phantom if it's possessed. The Scion religiously three-shotted Max-durability-spec Krogans and Batarians ON BRONZE for several months, they still have the tech burst resistance, they have nuclear suicide bombers, a unit which literally invalidates power-reliant characters, and a boss unit known for flying, shooting lasers out of its ass, and shooting through walls.
I hate the Geth just as much for being a pile of buggy, broken nonsense, but fighting the Collectors on Gold and Up is borderline-impossible for power-reliant classes without a seriously good team backing you up. Good luck on that ever happening when you're recruiting from the greater pool of PuGs.