The reference to "slots" is in fact referring to gear slots. So yes, he is outright saying it wears maiming gear. DRG's interesting position is that it wears heavier armor than the other melee; this comment is in reference to a previous statement of his made sometime around when SAM was revealed (don't ask for a source, I cba).
They did this before with him, when he was introduced at a fanfest wielding three Katana during Stormblood's initial reveal before the job was teased in 5.5 with Gosetsu and then later when they revealed the Othardian part of Stormblood.
Also just gonna drop this from the official twitter today—to further back up my claim that Estinien is still a DRG, they released his Endwalker render today:
https://twitter.com/FF_XIV_EN/status...13173678153729