This is actually false.
It is a fact that taking Shield Swipe off of the GCD improves Pld Dps on Bosses; however, the amount of Dps gained is marginal (as in nearly pointless, especially with the potency nerf inflicted on SW) and there are HUGE trade offs for this tiny concession. Without going into specific numbers, Mob tanking/enmity/mitigation/and dmg as well as general Tp consumption have gotten immensely worse on Pld because of this change.
Shield Swipe no longer acts as a stopgap for Plds, because it no longer delays their primary combos. There are now ZERO interruption to Pld Tp consumption (unless you include Flash, which does ZERO dmg and hurts party dps output), so they can burn their Tp bar like it's going out of fashion. This used to be a problem mostly for boss fights, but now it can be seen even in Mob tanking. Pld's no longer have the option of threading their Primary combos with Shield Swipe, so their RoH combo can only be interrupted by Flash. To hold aggro efficiently, they have now been restricted to using Flash more often which, again, hurts dmg values.
Mob tanking itself has taken a hit because of this. Pld's no longer have the ability to exploit Shield Swipe as a means of holding mob aggro. After 3.0 you could run into a mob, Shield Lob > Flash > and then cycle your RoH combo with Shield Swipes threaded in between each move (FB > SW > SB > SW > RoH etc). If you made sure you had RoH land on a different target every time, you reduced your overall incoming dmg using the debuff while maxing your enmity on that target. If you did the same thing with Shield Swipe (alternated a new target each time) you were maxing enmity while debuffing with Pacify. If you were doing a bigger pull you could pop Bulwark to make this rotation even more efficient. If you spread your enmity well enough using Shield Swipe, you could even forego the use of RoH after one or two applications in favour of Goring Blade to increase your Dps even further. It got to the point where, if you knew how to do this really well, a Pld needed no more than 1 or 2 Flashes to hold aggro and it was all about dealing pure dmg while increasing mitigation. For a blissfully short time, we weren't miles behind War's and Drks on holding mob aggro while outputting Dps and were even a little ahead in terms of mob mitigation because of Pacify/RoH applications. Now we can't do this nearly as efficiently.
TL;DR:
Pros of taking SW off the GCD: Minuscule increase to Pld Dps on Bosses
Cons: Reduced Enmity on Mobs. Reduced Dmg on Mobs. Reduced dmg mitigation on mobs. Increased Tp consumption without respite. Reduced efficiency and utility of Bulwark/Shelltron.
Verdict: Was taking Shield Swipe off of the GCD a "good" change? In short, no.