The level of incomprehensibility between Finnish, Estonian, and Magyar is quite interesting, suggesting a divergence dating back probably millennia
Agglutinative languages (Proto-Uralic is believed to have been) tend to wander off like a road in no time, which has led to a lot of reclassications, changing the branches of agglutinative language trees, and the like.
The extinct ancient agglutinative languages (Sumerian, Elamite, Kassite, and probably the Indus Valley/Harappan tongue) appear to be isolates, but as they’re only known from scripts, and their possibly unknown contemporary related tongues were never recorded, they may have managed to survive.
Correct. I speak Magyarul. If I hear Finnish or Estonian in the next room behind a closed door, the sounds do sound like Hungarian.....but if I hear those languages spoken, I don't understand a word of it. Hungarian is so totally different from any of the Indo European languages. It was a real surprise to me when I first went there in the early 90s and could not understand one single word. I was used to going all over Western Europe and understanding a lot of the words even if I didn't speak the language.