nah, he still easily solos
with his high-end feats and using the full potential of his weapon, he can slay non corporeal [to a certain degree] and intangible monsters like cui's
not to mention, he gets his powers from gaia deity danu and gets more zenkais, as the battle goes on, that means, regen like ability and immortality
[in his warp spasm mode, his attacks become even stronger and generates heat and sometimes he is imbuing the heat to the attacks to melt his opponents, plus his body analogy changes as well, means his pressure points and all, are reversed, similar to souther from hnken, he becomes a crazy raging like monster - still humanoid, and gets control over it, as the arcs progress]
not to mention, he has the gae bolg tech as well
since slaine is based on the irish myth of cu chulainn - barbarian edition