Beyond “what he sees” — disputing clarity itself
The phrase “Are you going to doubt (or dispute with) him about what he sees” conveys casting doubt and throwing conjecture upon what he sees — and also upon what he understands.
It is not only doubting the Messenger’s ﷺ direct vision of the Angel delivering revelation, but also doubting the way he sees reality, life and the truth; the way he sees the false religion, practices and excuses and cuts right through them.
His arguments are crystal clear. What position and truth are used to cast doubt upon the Messenger ﷺ when the Qur’an’s worldview is so powerful?