Does the extra bowing performed by the Imam compensate for the deficiency in bowing on the part of some of the congregants, and what is the ruling on the prayer of one who did not perform the deficient bowing?

The prayer of the congregants is invalid if they unknowingly missed a bowing in the first rak'ah and did not make it up or perform a substitute rak'ah for it. The extra bowing performed by the Imam does not compensate for the bowing missed by the congregants. The Imam's delay or omission of the sujud al-ba'di (prostration of forgetfulness after the salam) does not invalidate the prayer. Qunut in the Fajr prayer is a matter of difference among jurists; some consider it a Sunnah or mustahabb (recommended).