What they mean by "change the damage calculations of tanks"?

[Cynric]

In a vacuum it might be pointless, but the game doesn't exist in a vacuum and tank gear historically has STR on it on the left side, since *all* left side gear has one primary main stat and a secondary main stat (for most classes, the secondary stat is VIT, but the pattern is reversed for tank). In terms of coinciding with existing gear, they're more likely to do a split so they don't have to recalibrate the way stat budgets work for left-side tank gear.

Gear shared between Monk and Ninja had Dex and STR on it. Ninja didn't magically get stronger from the strength stat existing on that gear.

It's not really hard to say if Tanks don't need Str on gear then it doesn't have to be there. You're thinking too inside the box. Nothing is set in stone with game development. Especially itemization.