I actually find the post from Sam2 regarding the G-d not intending for us to understand certain things to be the best one so far on this thread.
As for the Rishonim that state certain things in Torah are Meshalim.
Yes they state them, however most of them are either written as “pshat” meaning a way to understand simply not not “pure emes” ( a distinction made by all rishonim when explaining Psukim ) and others were made without knowledge of Zohar.
The Ramban does come close to calling those approaches Kefira as do many others. The Vilna Gaon in particular is quite famous for his complete rejection of that mehlech was disproven when the zohar was accepted.