I share the same thoughts as you. I feel that Juventus did the best thing to fire Motta because the club is losing its momentum and before you know it, they might go down the table. However, hiring Igor Tudor is not a guarantee that he can maintain the fourth position till the end of the season.
What do you expect the management of a club that is as big as Juventus not being sure if they can make it to the Champions League after two consecutive humiliations by clubs that they're stronger than in previous seasons. A change of coach will be the only option, because it seems Motta is not getting it right in Juventus.
I agree that firing Motta was the right decision, I just don't know about the timing. This is too close to end of the season and they are at a sensitive part of the season, if we can do this then we could have a great period with Juventus finally doing awesome and then finishing higher.
But this is too late into the season and Tudor do not have that much time left, so I do not think it would be easy, he will have hard time fixing what the team is doing right now. Firing Motta was a late move, and maybe they shouldn't have done it for now, sure sack him right away as soon as the season ends, but doing it right now seems like a mistake to me, a risky move that may not give much fruit in the end neither.