The problem with your Levi being only 4star is that the speed differential between your Levi and a 7star Levi is too great for the Scimitar’s speed boost to let you overtake them.
As it happens, even if both are 7star, an r9 Levi will not overtake an r10 Levi with the Scimitar strategy either.
The only thing I can think of that might work is fielding Tie Reaper from the start. That causes the enemy cap ship to lose 15% TM when any ship is defeated. That and Scimitar first reinforcement might get you back ahead in the ult race, but it might not be enough.