“I am just exploring what appears to me to be black and white…”
Exactly. Looking for black and white is a symptom of being very literal minded.
To you there are two choices, either literal in the fullest sense of the way we do practice it today or non-literal, and it is code words to be deciphered like a dream and has no relation to what it says.
A good look in classical Sefarim well show you that everyone takes it at face value, that the Avos kept the Mitzvos. Otherwise, we wouldn’t have these discussions by the Ramban down about why Yakov married two sisters.
However (I guess that’s a ‘qualifier’ word), being of a different form — since they had the licence to fulfill things to their own understanding — means that although the Maamar Chazal means exactly what it says it still might not mean what you picture.
The Medrash says that Avraham Avinu figured out the Mitzvos. We also learn that Noach had a Kabbalah of which animals are Tahor. No, this doesn’t mean he was a nice guy. It means what it says. And yet, they still didn’t keep Teffilin the way we do. Yes, they literally kept the Mitzvos, but not all of them were practiced the way it was spelled out later on.
If they figured out Teffilin that means they knew the reason for it. They can then choose to fulfill this idea in whatever way made sense in those times.
You seem to be fine with the understanding that it just means that they understood Hashem and followed His will. This means that you understand that there is a purpose to all the commandments, at least as a group, and they fulfilled that function. Now, take this one step further. There is a purpose to each commandment as well. They kept that, too.
Teffilin d’Morei Alma are very real, it doesn’t just mean Chazal found a cute way to describe the fact that Hashem loves us. But being very real doesn’t have to connote physicality. The same way we know Hashem has a Kisei, which is real and still not physical, we are told He has Teffilin, which are obviously not physical, but they are real and Moshe Rabbeinu was shown Kesher Shel Teffilin.
Not being physical does not mean it’s a Mashal.
If you can’t wrap your head around this it’s because you are too literal-minded.