He is not holding him back. You see Kaidou, Bigmom, Doflamingo, etc in their introduction. And you see BB now. There is no point in holding him back when he is continuously on the move.
Honestly, I don't understand this tension concept, particularly for one piece.
You always know the protag will win when there are stakes like 'if not, everything is over'
And people had a myriad of discussions about how Luffy going to lose against Kaidou in the final round even though people keep on telling that there is 'no tension' in that fight.
And can you absolutely tell that if right now Luffy vs Kizaru happens who will win? nope.
So same way, it is pointless to discuss tension. What I want is competence from Blackbeard. The same kind of competence he has shown during timeskip and preskip.
More than tension, I am in anticipation on how the fight will go and end. Oda needs to succeed there. We all know Luffy will win against Lucci in eneis lobby but it became the best fight in one piece because of the execution from the beginning to the end. Luffy vs Kaidou 1 vs 1 almost had such execution except for the abrupt one-punch underwhelming climax.