Suggestions: increase speed for Treekin (I think bringing them up to 40 speed would work, though this isn't a solid number) and mark as treekin as "High Threat" entities (for those who don't know, when a splash-attack hits entities labeled as "high threat," just one of them will take all the damage from the attack, rather than the damage being spread out across all hit entities).
Basically, the problem currently with tree kin is they are defensive monstrous infantry: the idea behind them seems to be using their mass and high defensive stats to block high-mass enemies (i.e. SEMs and Cav) and basically tank damage from such enemies for the WE army, but they struggle to actually do this due to slow speed (34 speed is fairly slow for the WE roster) and how monstrous infantry work (i.e. the infantry fighting with the monstrous infantry tends to have more damage directed at them than the monstrous infantry, which works when the monstrous infantry is supposed to be the heavy hitter but not so well in the inverse).
Most people have advocated for swapping more of their defensive power for offensive power, but doing so undermines the purpose of the unit: they're supposed to be hyper-tanks that need help to kill enemies, not forest trolls/chaos spawn with a tree skin. Instead of trading defense for offense, why not give them the tools they need to do their job?
Increase their speed so they can actually block/pin high-mass enemies and change them to "high threat" so they actually tank damage from such enemies instead of the infantry taking it. Do this and tree kin should become much more viable outside of tree-blobbing (and to prevent said tactic from being buffed by this just swap the MD increase in woods to a speed buff while in woods for these abilities). Additional improvements could be added (i.e. increasing their mass or size) if necessary, but these two buffs will allow them to fulfill their purpose without compromising their identity.