The attack is not 288% * 6 but 251% * 6 for level 10 Sonic Strike xD
That’s a huge damage difference.
But yeah, Rush Dog isn’t that good.
Level 15 doesn’t even deal twice the damage of level 1 [ 1110% vs 630% = 1 : 0,57], so it’s a total waste of points just for killing a few bosses. Non-bosses will die easily when you have a high Coursing/Snatching/Retrieve level instead.
I just have level 1 Rush Dog for damage + stun[saves a lot of SP, 38 instead of 100], spreading my points throughout the other skills.