So I finally got Helbindi and fed him to my Soren.

Just right after I made him level 40, I gave his A skill immediately. It took me some orbs, especially after that Sanaki pitybreaker (no greens that round). So I can keep Soren in my core without worrying about Arena score that much anymore, since he's +10 as well. And here he is.

PS. I tried Watersweep with him and made him a dragon poker, since I have harder time with them than nondragon armored units, and it was effective. Alfonse is my current bonus unit and he has no problem doing last hits.