I love the companion system but feel the choice of just the 2 and how they react to certain situations or actions you do somewhat limits how and when you have them out. If you want to have Bastian out you better not steal or murder (Blade of Woe) ANY NPC including enemies. Where as Mirri is okay with stealing/thieving but hates Blade of Woe acts against ANYONE also. Bastion being inline with the Mage's Guild and Mirri with the Fighter's Guild doesn't make sense to me. IMO, as a DK, Bastian should be aligned with the Fighters Guild and Mirri as a NB the Thieves Guild.
That would enable a companion to be introduced that aligns with the Mage's Guild (a Sorcerer) and/or a companion that favors "evil" acts. Also, Bastian's attitude towards situations (and his conversations) seem to be more on the Templar front than as a DK. He talks and reacts as a "holier than thou" companion.
To be the man you have to beat the man.