I came across this example sentence on spanishpod101 and just wanted to confirm that this is an actual idiom that is commonly used?
The sentence was:
Más me gustan las milongas de aquel entonces a los nuevos tangos de hoy.
From which I deduced the pattern "más me gusta X entonces Y" to mean "I much prefer X to Y". I could not find any such use for "entonces" in the dictionary hence my doubt that this could have been an error in the note?
There is no error in the sentence. The pattern is "más me gusta X a Y" (meaning, as you have deducted, "I much prefer X to Y"):
Más me gustan X=(las milongas de aquel entonces) a Y=(los nuevos tangos de hoy).
Note that the sentence is comparing two kind of dances from two different periods of time:
Los nuevos tangos de hoy.
Las milongas de aquel entonces.
The use of entonces must not be separated from de aquel, as de aquel entonces is an expression that means "from that (period of) time". Other similar constructions are:
Más me gustan las milongas de aquel entonces a los nuevos tangos de hoy.
What you didn't realize is that here, entonces is a noun. It means "period [of time]" but with a flavor of nostalgia.
Still, the construction being used, Más me gusta X a Y, is a bit unusual. I see it as a variant of the more common construction
Prefiero X a Y.
(which is the one I recommend you learn, as a pattern, for expressing your ideas).
Here are a couple of examples taken from linguee.com for this construction:
Por lo que respecta al espacio, prefiero esta oficina a la anterior.
Prefiero la literatura contemporánea a la clásica.
