A lot of Gladiators focus their stats on vit only and then maybe str for increased blocking. Mrd can put a lot of points in dex and str, while still having a higher healthpool than Gla.
Having a bigger healthpool and higher evasion on top of the stronger emnity & damage (Storm's Path every 10sec) is why I find Mrd better in defense on multiple targets. ... unless all the monsters want to stand right infront of the Gla, but that doesn't happen a lot.
And I'm under the impression that Defender 2 is stronger on Mrd main class, but haven't been able to prove it yet.