How were the Salaf able to attain khushūʿ (devotional humility/concentration) in their prayers despite performing hundreds of rakʿāt (prayer units) daily with speed?

The swift recitation of the imams does not necessarily indicate a lack of devotion; rather, they are presumed to be diligent in it. The blessing of worship, prayer, and the Quran causes a blessing in time. Indeed, Ibrahim ibn Abd al-Wahid al-Maqdisi said that frequent recitation of the Quran facilitates the pursuit of knowledge, and الضياء المقدسي experienced this. It has been narrated from the Salaf that increasing one's portion of the Quran (hizb) adds blessing to time, and this might be a miracle from Allah for them.