Tell that to the failure rate for sub-15 keys. MSV is certainly capable of doing 15’s. Well beyond 15’s, in fact. But the fact remains, the more capable a spec, the more that spec is able to cover for the failings, inadequacies, mistakes, and inexperience of others.
If someone accidentally overpulls, a fire mage can pop combust and melt the pack. Might set the timer back slightly if it shuffles their cooldown timing, but it saved a wipe. If that fire mage were instead, say, a feral druid or a demo lock…now that overpulls may instead turn into a wipe. And maybe that breaks pathing because a skip you used can’t be easily repeated. And the entire run falls apart.
Again, it’s not just some minimum threshold where DPS above that is useless and unnecessary. That extra DPS helps against mistakes and error. It quickens fights, which reduces the window for those mistakes, and eases the burden on the healer. Maybe it even let’s you 2-chest what you’d only 1-chest, or be able to still time it after that bad wipe or accidental reset or death without a BR.
And that’s just on the DPS side. Utility and control are equally vital. While SV brings a stun, so does BM, and MM brings a knockback and brings Binding Shot without having to sacrifice Posthaste. MM and BM are also both less susceptible to incidental damage and deaths due to not being in that quite-a-bit-more-hostile melee radius, and are better able to apply their DPS, since they don’t have as demanding positioning requirements.
Where you may have to stop DPSing and run out to avoid things like the pools on Hakkar, the statues on Lord Chamberlain, or stun circle on Domina, the whirlwind on the Theatre trash, or the knockback circle on the Mists maze trash, ranged DPS just keep on murdering.
There’s a reason ranged DPS are preferred in most PvE content. They’re simply more flexible.
It’s not just about speed, it’s about tolerance for mistakes and variance. If you’re right at that minimum threshold, a single mistake burns the run. And if the MDI has proven anything, it’s that even the very best players in the world make mistakes, and need to have the buffer room to handle them. Amplify that even more for players further down the skill spectrum.
Basically, there isn’t some magical “enough” beyond which everyone is functionally equivalently useful. More DPS is always helpful.