Well, if you compare roles, Cortex and Armada just mix their roles a bit differently, causing Cortex to have one extra unit.
Marauder - Amphib raider VS Shiva - Amphib Assault
Razor - pure land antispam/dmg VS Demon - pure land antispam/dmg
Vanguard - all-terrain & siege VS Karg - All-terrain & antispam VS Catapult - pure land siege
Thor - big land tank assault VS Behemoth - big land bot assault
Titan - big amphib assault unit VS Juggernaut - big amphib assault unit
When it comes to metal sinks, it would make more sense to compare build power requirements, how quickly you can dump metal into them to get out big units.
Per 100 build power:
Juggernaut is 5.2m+111e per sec
Titan is 4.9m+104e per sec
Behemoth is 3.2m+81e per sec
Thor is 3.6m+96e per sec
So they're not actually that different and Titans aren't a big liability like Juggernauts and better speed and damage, so in some ways they're a better metal sink than Juggs.
Actually one of the fastest ways as Cortex to spend your metal is Dragons: 6.1m/86e per sec. Hornet on the Armada side is 5.2m/92e per sec. But those options are shredded by fighters, so also the fastest way to lose your metal investment if the enemy has fighters or lots of aa.