That is generally true as a philosophical statement but in rogue case both outlaw and assa are being played up to the top echelons of progress. If a raid leader wants to slot a leather melee into the raid dh / rogue are decent choices, feral / monk are very situational and often sub-optimal choices.
Smart Raid Leaders care not only about which class parses best on paper, but also which player dies less (rogues are good at surviving), which player has more consistent dps (that's why assa > outlaw because outlaw has big variance one pull you do amazing another you do meh), which player can deal with mechanics easier (less dps lost, less chance of dying) and even things like armor type and tier token distribution (even if DH is a bit better than rogue you don't want to have 4 DHs in your raid team unless you're one of the guilds which raids on alts and class stacks fight per fight basis, and people have multiple classes to boot).
The "but rogues are pure dps" argument doesn't mean much because you aren't keeping your dps DHs, Warrs, DKs and whoever else "because they can tank too", most guilds will have 2 main tanks and maybe 1 or 2 backups tops, not half your melee team.
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I'm in a 9/10m guild and I have friends in a world top 200 guild who have mythic Gul'dan on farm, both guilds have 2 rogues on the roster and I didn't see in either case rogues being benched for being rogues. The fact they can survive being a backup emergency soaker for Elisande orbs or getting hit by rings while other class might die makes them not a bad choice for that boss, and for Gul'dan they're the preferred soul soakers.
The only NH boss you might have wanted to bench the rogues was spellblade progression because in that boss fast aoe is more important, on every other boss even if it has aoe involved it's not so crucial every single dps in the raid aoes instead of sitting at the boss.
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It's not useless because in case of most NH bosses the extra padding some classes can do inflates their parses but contributes very little to the actual killing of the boss. The fact assa spec is based on bleeds also allows you to keep some of your boss dps running while you do other stuff like soak swirls on krosus or hide behind pillar on tichondrius, while some other melee can't do that at all.
Tbh half the fights the raid leader's headache is "how to make my dps hit the important target instead of padding until cows go home". If a class doesn't have easy padding built-in doesn't make it immediately useless. On the other half, look at monk, tons of passive cleave and very meh single target output even post rising sun kick buff.