Is the Tabligh Jamaat's congregational loud and lengthy dua at their annual Ijtima' Bid'ah?

Answer

You have not understood the meaning of Bid'ah. Nothing may be added to or deleted from a Masnoon practice. For example, making Khatam of the Qur'aan is a Masnoon practice. It is an ibaadat for an individual, not a congregational act of worship. Thus, making a collective dua after making khatam of the Qur'aan is bid'ah.

Another example: Visiting the graves is Sunnah. But to lift the hands and make a Dua there whether individually or collective is bid'ah since lifting the hands at the grave is not Masnoon. All Masnoon acts of ibaadat should be retained in their original form. The Tabligh Jamaat's bayaan or its methodology is not Masnoon. It is mubah (permissible) as long as the prescribed limits of the Shariah are not transgressed. Just as its bayaan is mubah, so too is its congregational dua, mubah. This dua is not attached to any Masnoon act of Ibaadat, hence it is permissible because it does not change any Masnoon act of Ibaadat.

However, if the Tabligh Jamaat begins to teach that their congregational dua is Waajib, then it will also become bid'ah because of elevating the mubah status to wujoob.