Reflecting long enough to consider what it means to be the Founder of our faith, which is also called the Way of G-d, you will have your answer.
The word Founder in English comes from the verb found which according to the New Oxford American Dictionary means:
To establish or originate something especially by providing an endowment.
This same dictionary explains that Endowment means:
An income or form of property given or bequeathed to someone.
That same dictionary explains that Judaism is the monotheistic religion of the Jews...looking to the biblical covenant made by G-d with Avraham and to the laws revealed to Moshe and recorded in the Torah which established the Jewish people's special relationship with G-d.
Judaism was established neither by Avraham, nor Moshe. But rather it was established by G-d directly as is stated explicitly in Bereshit 18:19, which says,
כִּ֣י יְדַעְתִּ֗יו לְמַעַן֩ אֲשֶׁ֨ר יְצַוֶּ֜ה אֶת־בָּנָ֤יו וְאֶת־בֵּיתוֹ֙ אַחֲרָ֔יו וְשָֽׁמְרוּ֙ דֶּ֣רֶךְ יְהוָ֔ה לַעֲשׂ֥וֹת צְדָקָ֖ה וּמִשְׁפָּ֑ט לְמַ֗עַן הָבִ֤יא יְהוָה֙ עַל־אַבְרָהָ֔ם אֵ֥ת אֲשֶׁר־דִּבֶּ֖ר עָלָֽיו׃
That I (meaning G-d) connected with him (meaning Avraham) in order that he 'command/connect' his children and his household after him that they will keep the Way of G-d, to do charity/righteousness and equitable judgement. For the sake of this, did G-d bring to Avraham that which He spoke to him.
And this same idea was later expressed by Moshe Rabbeinu in Devarim 8:2, which says,
וְזָכַרְתָּ֣ אֶת־כָּל־הַדֶּ֗רֶךְ אֲשֶׁ֨ר הֹלִֽיכֲךָ֜ יְהוָ֧ה אֱלֹהֶ֛יךָ זֶ֛ה אַרְבָּעִ֥ים שָׁנָ֖ה בַּמִּדְבָּ֑ר לְמַ֨עַן עַנֹּֽתְךָ֜ לְנַסֹּֽתְךָ֗ לָדַ֜עַת אֶת־אֲשֶׁ֧ר בִּֽלְבָבְךָ֛ הֲתִשְׁמֹ֥ר מצותו אִם־לֹֽא׃
Remember the entire way that the L-rd your G-d has conducted you in the wilderness these past forty years, that He might test you by hardships to learn what was in your hearts: whether you would keep His commandments or not.
And this is even hinted at through one of the special traditions given to the Scribes when writing a Sefer Torah.
The phrase, Way of G-d, in Hebrew is דרך יהוה, like is seen in the cited text from Bereshit above, has a gematria (numerical value) of 250 which is נר (meaning the gematria of Ner, light or lamp, is Derech HaShem).
After the sin of the golden calf, when the Jewish people had returned to G-d's way, G-d renewed his covenant with the Jewish people revealing to Moshe, our teacher the inner essence of His Torah what are called G-d's 13 attributes of Mercy. This is recounted in Shemot, chapter 34 beginning at the fifth posuk.
The Scribes were given a special tradition to write two oversized letters, the letter Nun and the letter Reish at these passages, beginning with the Nun of the word נצר (It should be noted that נצר is also understood to allude to רצון, G-d's will.) in Shemot 34:7 and ending with the letter Reish of the word אחר in Shemot 34:14. That what is restated and renewed in these passages is the Way of G-d. That this is what is intended, that the Jewish people are to be a source of light to the nations like is expressed in Yishayahu 49:3-6.
And this is also in keeping with what is expressed by Proverbs 6:23 which says,
כִּי נֵר מִצְוָה וְתוֹרָה אוֹר וְדֶרֶךְ חַיִּים תּוֹכְחוֹת מוּסָר׃
For the commandment is a lamp, The teaching is a light, And the way to life is the rebuke that disciplines.
See Ibn Ezra to this posuk for additional insight.
And restated again in Proverbs 20:27 which says,
נֵ֣ר יְ֭הוָה נִשְׁמַ֣ת אָדָ֑ם חֹ֝פֵ֗שׂ כָּל־חַדְרֵי־בָֽטֶן׃
The soul of man is the lamp of the L-rd Revealing all his inmost parts.
See Rashi to this posuk for additional insight.
It should be noted that the highlighted section of the Torah mentioned above, Shemot 34:11-14 deals specifically with the subject of possessing the land of Israel which is the provision of the endowment aspect of the dictionary definition associated with founding something.
The first link of resources in your question is to an English article by Rabbi Tzvi Freedman with Chabad.org. Although Rabbi Freedman incorrectly uses the English term Founder with Avraham, he does indicate what he means by the expression by footnoting it to Mishnah Torah, Hilchot Avodah Zarah, 1:2-3.
If you look to that source, you find that Rambam does not call Avraham the Founder of Judaism (מייסד יהדות). Rather, he refers to him as the Pillar of the World (עמוד של עולם).
This phrase is making the allegorical comparison of Avraham to the pillar of a building which prevents the roof from collapsing. And this is how the Torah explains the importance of Avraham in relation to the creation of the world, like is found many places in the Torah.
Rambam explains that Avraham figured out that the premise of idol worship in his day was wrong and he rejected it. He goes on to explain that Avraham taught that any worship should only be directed to the Creator of everything and that this Creator is the only G-d, there is no other. And Rambam explains that Avraham addressed the Creator with the name El Olam as cited from Bereshit 21:33.
It is worth noting that this is not the name of G-d generally used in Jewish prayers and blessings, like the Amidah prayer.
But Rambam, at the conclusion of halacha 3 cited above explains that everything which Avraham taught was in the process of being lost when his descendants descended into Mitzrayim. He explains that if not for G-d keeping His promise to Avraham, this would have happened. And Rambam explains that G-d chose Moshe to be His Shaliach, His legal agent, and through Moshe, our teacher, made Avraham's descendants aware of how to worship Him.
In other words, Moshe communicated what G-d established together with G-d's endowment of the land of Israel.
I was unable to determine who the authors were for History.com or Religions.com, but neither are traditional, Orthodox Jewish sources. As far as I was able to determine, the editors of The New Jewish Encyclopedia were both Reform Jews, which is again, not a traditional, Orthodox Jewish viewpoint.
