Quranista are not only ne group but many groups with different claims, so we can not generalize the rule on all of them before knowing what exactly they claim.
Those (Quranists) who deny or reject every Hafeedh is away from Quran because Allah in Quran did order us to take the meaning of Quran from the Prophet (SAWA).
Please write about the faith of the group you mean to unable me to reply.
Wassalam.