I disagree with the assessment that it's slight because it can reduce the incoming damage by 10%. The damage reduction is just about fine, it's just that we can get away without it. Even if it was 20% or 30% mitigation, nobody would care because we use Rampart, Sentinel and Sheltron on the busters and have the defense stat and a trait that reduces damage. Tanks survive mechanics that everyone else in the raid can't, including ones that are supposed to wipe the entire party, so why would they need yet more mitigation? Additionally, once you gear up as weeks progress, the extra Vitality makes up for not having Tenacity by giving everyone more room for error. When you combine these facts with how it increases damage less than Determination, a lot of people will choose the piece with Determination on it over the piece with Tenacity on it.
If someone is of the mindset to help the healers as much as possible with the Abyssos dots at the expense of their damage, they already have plenty of reason to stack Tenacity, but let's be honest, everyone just goes to The Balance or their friends reiterate information from there to avoid Tenacity, so they will avoid it even if it's 20%, 30% or 40% mitigation. They can say "it could be useful for prog" but people will just skip past that, seek out a BiS list and use it.
Skill/Spell Speed increases the damage of dots/damage areas and auto-attacks as well. I don't think that this stat is actually a problem itself. The problem is that we have strict rotations that can be messed up by using it and there will always be a meta, and that meta is regarded as being crit. If we got rid of crit and dh, jobs without too strict or unaffected rotations might actually use it.Skill/Spell Speed - A stat that determines your GCD. Definitely needs looking at, as its only purpose is to enforce certain GCD tiers and not provide much else. It's been the bane of some jobs' existence as well.
There will always be a meta stat, especially while we have crit and dh available to all jobs. Without those it would probably be different stats for each job.