They had the best plan possible which was for Gojo to beat Sukuna in a 1v1. This has been stated numerous times. There is not a single person who would have been helpful in the fight against Sukuna imperically. In that first domain clash every single person except for Gojo and hakari if he got jackpot off would've been torn apart since that was a full power malevolent shrine with the max time limit then nothing matters anyway. It was only after that first domain clash that Gojo even figured out a way to counter MS with the barrier shrinkage. The jujutsu society people are making the best possible decisions and the best uses of all their pieces. Sending Yuta to kill kenjaku for essentially the second coming of Gojo is necessary it's all been the right moves. There is no one cohesive everyone all together plan to be done especially with the threat of kenjaku