No, this is a great question!

Lord Arianthus is good to act as a Tank in the First position in a similar way as one would use the "Peaceful Giant" card from the Neutral Splinter. However, at Level 3, he's quite a powerful Tank with the four following abilities:

Shield - Reduced damage from Melee and Ranged attacks.
Void - Reduced damage from Magic attacks.
Magic Reflect - When hit with Magic damage, does reduced Magic damage back to the attacker.
Thorns - When hit with a Melee attack, does damage back to the attacker.

Now, non-attacking Tanks aren't as useful for every rule-set (like when all Monsters have the "Sneak" ability) but he's an amazing Tank choice IMO once he's upgraded to at least Level 3.

Thanks for reading!