Is the Ran an apikores, by his own definition?

There is a famous statement of the Ran, in Derush 5 of Derashot HaRan. In English, the beginning of it is (apparently in the alternative version of derush 5, whatever that means):

“As we were commanded to follow the consensus [of the Sages] in the laws of the Torah, so we were commanded to [follow] everything they say to us from the aspect of tradition [Heb. al ẓad ha- kabbalah], from among ideas and midrashim of [Scriptural] verses, whether that statement is a miẓvah or not. A Jew who deviates from their words — even in that which does not pertain to explaining miẓvot — is a heretic [Heb. appikoros] and has no share toward the World to Come.”

You can read this statement in Hebrew, with the context following it, here.

However, I would like to call attention to another statement within Derashot Haran, from his Eighth Drush. In it, he acknowledges a midrashic statement, but almost dismisses it as al tzad hadrash, and proceeds with his own statement about the reality of the world, based on what he feels to be peshat.

I am open to suggestions of why this does not make him a heretic who has no chelek in Olam Haba (just like many of the medieval commentators of peshat and derash who offered interpretations of pesukim which were at odds with the interpretation found in Chazal).

"But the answer is that the effects which reach in this lower world are not on an individual basis, via individual causes, but via general causes. For it is not the will of Hashem Yisbarach that He change nature for each individual.

And when Hashem Yisbarach wished to smite the firstborn of Egypt, He innovated some matter which harmed which was associated with being a firstborn. For the firstborn have an association between them in general which connects them. And this is that there is no doubt that the womb which has never birthed a fetus does not have the precise features of a womb in which fetuses have already been formed. And by aspect of that difference, it is possible that there was in all the firstborns a preparation to receive some matter which was concealed from them. And because of this, the commandment of sanctifying the firstborns depends upon the {first} opening of the womb. For the status of firstborn gives an association and connection between the firstborns, and there is no firstborn to the father at all.

And even though they said in a midrash {about those Egyptians dying in the plague} that "if there was no firstborn, the eldest of the house was called the firstborn {and died}," this is by aspect of derash. But according to the peshat of the matter, the firstborns were dependent upon the {first} opening of the womb -- they were the ones who were smitten.

And if there was among them an association and connection, by virtue of this association, it should have been that the firstborn of Israel also would have died, if Hashem had left them to their nature. And because of this, Hashem Yisbarach said that because He protected them and saved them from the evil that was fitting to befall them, sanctify them to Me."

Here ends my quote of the Ran. To cite Rashi on Shemot 12:30,

for there was no house in which no one was dead: If there was a firstborn, he was dead. If there was no firstborn, the oldest household member was called the firstborn, as it is said: “I, too, shall make him [David] a firstborn” (Ps. 89:28) (Tanchuma Buber 19). [Rashi explains there: I shall make him great.] Another explanation: Some Egyptian women were unfaithful to their husbands and bore children from bachelors. Thus they would have many firstborn; sometimes one woman would have five, each one the firstborn of his father (Mechilta 13:33).

כי אין בית אשר אין שם מת: יש שם בכור מת. אין שם בכור, גדול שבבית קרוי בכור, שנאמר (תהילים פט כח) אף אני בכור אתנהו. דבר אחר מצריות מזנות תחת בעליהן ויולדות מרווקים פנויים, והיו להם בכורות הרבה, פעמים הם חמשה לאשה אחת, כל אחד בכור לאביו:

So Ran is dismissing a Midrash Tanchuma, and working with a peshat of his own making to describe reality. And even if you say he is interpreting it instead like the Mechilta, you are in trouble, because the Mechilta interprets this pasuk as there being a bechor to each father. So Ran is explicitly at odds with the first midrash, and implicitly at odds with the second.

So what does that mean for us? When Ibn Ezra says that kavata means "her tent," such that Zimri was in his tent and Cosbi was in her tent, such that Pinchas' action was not beshaas tashmish and he did not strike them both through with one blow, would the Ran consider him an apikores? How is this peshat intepretation different from Ran's own peshat interpretation here?

When Ramban argues with the midrash and says that ויבא when Avraham came to mourn Sarah refers to his coming to her tent, rather than the elaborate midrashic explanation, would the Ran consider him an apikores? How is this peshat intepretation different from Ran's own peshat interpretation here?

There must be some nuance here, and I would guess that this nuance can be quite helpful.

Elsewhere, he argues with midrash about what the דור הפלגה was doing. Perhaps I'll make another post about that. It seems that he felt that one could argue on midrash.