Does not following the Sunnah in ablution—such as wiping the head and ears three times with a lot of water—invalidate the ablution and prayer, and is it permissible for someone who does that to lead the prayer?

Wiping the head is an obligatory act among the fard (compulsory) acts of wudu (ablution), and it is not recommended to exceed one wipe, performed by bringing the hands forward and then backward. This is the view of the majority of scholars and is the most preponderant opinion, although Imam Al-Shafi'i recommends wiping twice or thrice. Whoever does so, their wudu and prayer are not invalidated, and it is permissible for them to lead prayers. Such a person should not be criticized if they are following a scholar who permitted that. One should not rush to criticize, especially in matters of scholarly disagreement, because the person might be following a jurisprudential school of thought that the critic is unaware of.