User blog comment:Lesdin/Darssan, the Inciter/@comment-7709681-20160223140120/@comment-7709681-20160223212814

The gameplay problem it presents is that you over-compensated the lack of reliable offense because of the possible damage output provided by Carve the Soul, since you could not add more damage into the kit, gating his reliable damage output.

If the latter statement isn't enough, having an insta-kill on such a short cooldown (Down to 33s) and eventually have enough reliable damage and enough defense so sustain yourself to build up Tarnished Heart towards late-game should, then should be. And now that you mention that the intention is to be build as a Juggernaut, then you're granting too much utility for himself to a nearly defensively builed champion (which further enhance his defense).

Not having enough burst or reliable mobility as an assassin to get out fast or enough AoE DPS to make yourself relevant in teamfights, just someone that sits on you by being too tanky, move too fast and constantly slow you until you can instantly get killed by Delusional Heartbeat and then walk fast to escape, and sits on the back line because he's only a damage sponge that cannot get focus on himself because he has no AoE DPS or relevant CC, which means that his tankiness only works for his kills.