Only if you design them to be.
Or alternatively, you can design them to have differing playstyles based on what they're doing.
Such as having "Tank Stance" offer skills that react to incoming damage. Such as how Shield Swipe works, how TBN can provide extra resources when used to mitigate damage.
You know... Tank stuff. Where you mitigate damage and are rewarded for doing it well.
While you make "DPS Stance" offer more skills that function best when you're not being hit in the face by the boss. Skills such as Cover/Passage of Arms which requires you to position yourself in a way that would be detrimental if you were getting cleaved by the boss. Maybe skills with Side/Flank/Rear positionals to get bonus damage in a similar amount to how the "Tank Stance" exclusive skills do.
You know... Actually designing the role to play into its role.
Not just sticking Damage+/Defence- and Damage-/Defence+ modifiers onto braindead DPS.
Such a thing was not done for "Weight" but to emphasis a point that has been either missed or ignored by someone.
Given that the statement in question was one that was a fundamental problem that has existed from the very beginning of the implementation of "Tank Stance vs DPS Stance" and is one of great importance when it comes to actually making Stances relevant in any way, shape or form.
Since, otherwise you get things such as:
Things that anyone who's ever played at max level should know.
That, because Tank stances offer a penalty to Tanks, that they're used as little as possible. Where ideal play is literally to just pull and use like 2-3 GCD's and then leave it. Where Tanks can be considered "Bad at pulling" because they need to use an extra 1-2 GCD's before they are able to sit in DPS stance for the rest of the encounter.
As such, if Tank Stances are designed in a way where they're giving damage penalties, they will continue to not be used.
If you design "MT" and "OT" Tanks where they are in default "Tank" and "DPS" stances and only offer CD's where they can swap over, then you'll simply never see "MT" Tanks played and everyone will use only "OT's" and only use the CD on the pull if it provides a boost in enmity (Which you didn't specify if it would. If it didn't, the skill would simply never be put onto anyone's action bar)