is also super stupid to make the Stranger Gandalf. FTR, I have no idea who the Stranger will end up being in the show, so this is all speculation based off Tolkien's writings. They are dropping MAJOR Gandalf hints in previous episodes, and I have no idea if that's to throw us off or to just prepare us. No idea. Anyway...

For starters, Gandalf in every account arrives well into the Third Age (nearly 1000 years into the TA) and he specifically arrives last of all the 5 Istari. He has no role at all in the Second Age, and Gandalf himself very specifically said that of all the places he's been to in Middle-earth, "to the East I go not." Anyway, making the two Istari the Blue's just makes so much sense from so many viewpoints...which is indeed probably why they'll make the stupid choice and make it Gandalf. But alas, I still hold out hope. Below is some info from Tolkien on the Blue Wizards, and you'll see some of this info has already made its way into the show:

𝐓𝐡𝐞 𝐁𝐥𝐮𝐞 𝐖𝐢𝐳𝐚𝐫𝐝𝐬

Alatar and Pallando are perhaps the most mysterious of the Istari, sent to Middle-earth by the Valar around the year T.A 1000 (later writings indicate S.A). Their mission, like the other Istari, was to combat the rising power of Sauron. They traveled into the East and South, far from the known events of the western lands.
In early writings, they may have succeeded, or failed succumbing to corruption or becoming lost to history. However, later writings suggest that they played a crucial role in sowing dissent and organizing resistance against Sauron’s influence in those distance regions.

𝐏𝐚𝐬𝐬𝐚𝐠𝐞 𝐟𝐫𝐨𝐦 𝐔𝐧𝐟𝐢𝐧𝐢𝐬𝐡𝐞𝐝 𝐓𝐚𝐥𝐞𝐬 𝐨𝐟 𝐍𝐮́𝐦𝐞𝐧𝐨𝐫 𝐚𝐧𝐝 𝐌𝐢𝐝𝐝𝐥𝐞-𝐞𝐚𝐫𝐭𝐡, 𝐏𝐚𝐫𝐭 𝐅𝐨𝐮𝐫 "𝐈𝐈 𝐓𝐡𝐞 𝐈𝐬𝐭𝐚𝐫𝐢"
Of the Blue little was known in the West, and they had no names save Ithryn Luin "the Blue Wizards;" for they passed into the East with Curunír, but they never returned,... pursuing there the purposes for which they were sent; or perished; or as some hold were ensnared by Sauron and became his servants, is not now known.
Note 3: In a letter written in 1958 my father said that he knew nothing clearly about "the other two," ... "I think," he wrote, "they went as emissaries to distant regions, East and South, far out of Númenórean range: missionaries to enemy-occupied lands, as it were. What success they had I do not know; but I fear that they failed, as Saruman did, though doubtless in different ways; and I suspect they were founders or beginners of secret cults and 'magic' traditions that outlasted the fall of Sauron."

𝐏𝐚𝐬𝐬𝐚𝐠𝐞 𝐟𝐫𝐨𝐦 𝐓𝐡𝐞 𝐏𝐞𝐨𝐩𝐥𝐞𝐬 𝐨𝐟 𝐌𝐢𝐝𝐝𝐥𝐞-𝐞𝐚𝐫𝐭𝐡 "𝐋𝐚𝐬𝐭 𝐖𝐫𝐢𝐭𝐢𝐧𝐠𝐬"
The ‘other two’ came much earlier, at the same time probably as Glorfindel [~S.A 1600], when matters became very dangerous in the Second Age. Glorfindel was sent to aid Elrond and was (though not yet said) pre-eminent in the war in Eriador. But the other two Istari were sent for a different purpose. Morinehtar and Rómestámo. Darkness-slayer and East-helper. Their task was to circumvent Sauron: to bring help to the few tribes of Men that had rebelled from Melkor-worship, to stir up rebellion … and after his first fall to search out his hiding (in which they failed) and to cause [?dissension and disarray] among the dark East … They must have had very great influence on the history of the Second Age and Third Age in weakening and disarraying the forces of East … who would both in the Second Age and Third Age otherwise have … outnumbered the West.

I got most of the above text from a LOTR Facebook group. They put it together rather nicely so I copied and pasted it.