Nope, they fixed that bug pretty fast.
Yeah, apparently the objective didn't work as intended in the beginning. I managed to get Roblin down in a similar manner with VtD and then just finished off the last 1% with Blade, got the awakening and ascension. Then I tried with my second account immediately afterwards, but got nothing and had to redo the fight with only Blade on the team in order to finish the objective.
It's not a particularly hard fight since Stellar Blade has got enough DOT to circumvent the main node, but he's also not a ramp champ that seems to be aimed at that type of content (or at least that's my feeling so far), so it's a really long fight. I ended up using a couple of revives, but it's not too bad all things considered.