Keep in mind that MRD also has a large HP pool, and is capable of wearing the same tanking gear we can, minus the shield. They get more DPS, and can easily hold hate just as well. They also receive full benefit from Defender II and have great Emnity generation.

Sure, Deflection and Aegis Boon II are good skills, but with a 60 second cooldown and 15 second activation time you can't say Aegis Boon II alone makes GLA better tanks. You would need to use the 3 skills you mentioned all at once to have a chance of completely negating all damage you receive from an NM. And you can only do it once every 60 seconds for 15 seconds. Sure it is nice, but that doesn't mean MRD Tanks die without these skills. They have a lot more HP than GLAs do with Capped Vit. I think that more than makes up for 15 second damage negation.