Brothers Nouman Ali Khan and Omar Sulaiman are liberals and moderates.
They rarely focuss on the Prophetic methodology of Dawah- i.e. focussing on Tawheed and eradicating Shirk and Bidah. This is their biggest problem.
Also- they’ve a tendency to hide/silently misinterpret Ahadith that do not fit the narrative of modern Islam .
Ustadh Nouman Ali Khan doesn’t follow the Sahaba’s methodology in teaching the Quran. He focusses on Arabic language and grammar to explain the Quran rather than the classical method of interpreting the Quran from -the Quran-then Sunnah-then by Sahaba- then by Arabic language.
Added to that Brother Omar Sulaiman constantly uses weak and fabricated stories in his Tazkiyyah classes.