don't fool yourselves guys the stats seem to say that the Rook on Tassadar's team was nearly worthless and just fed the enemy team without accomplishing much himself. the Regulus at least got some decent Assists in and probably helped out Tassadar racking up those kills. its usually the other way around though, Reg gets more Kills than any other DG if played well. long range, burst damage, finishing moves, Reg should have the most kills normally.
you can also see from those stats the Real Reason why Tassadar's team lost. nobody had any buildings down. really strange for Reg or Rook to fail to knock down a single building since they're both so good at it. the Rook on the other team was a machine, killed 10 towers and obviously that made all the difference.