To provide perspective the topic came up for myself when I wanted to explore debuff builds as far as I could as an avenue of scaling damage and defenses different than typical tried and true approaches (+dmg, procs, def soft-cap, a sprinkle of -res). The initial thought was cumulative -tohit -dmg -res from debuffs and a good IO build should be capable of taking and dealing a lot of damage, and it does! But only if the critter is a giant monster (counter-intuitive much??). Instead when I run a +4 it's half as effective or more, which ends up being massively less effective like with defense. There's this split in the content where debuffs are very effective or not worth specializing in which feels arbitrary and build limiting. In a team setting you will not carry the team with debuffs (maybe an AV, especially -regen), though you will make a difference for an already strong team.
Sure you can run some -res here and there and get a small damage scaling increase, but the more you invest (especially as an individual) the less relative gains you get like with most scaling factors, going all-in is counter-intuitive when your efforts are halved 4 days of the week (read: arbitrary) and my opinion is this lowers character diversity.
Debuffs are arguably more difficult to play with yet are punished more. You have to apply the debuff before getting any benefit. Buffs are generally always active and happen to scale much better. Take defense and tohit for example. If you cap defense with -tohit you need roughly -90 tohit (good luck) for +4 but if you cap with actual defense instead you only need 45. There's a near 100% difference in the numbers you need to reach cap based on what you happen to generally be fighting: +0 or +4.