The nuances of the limiting modifier "only ever"

I have heard and seen "only ever" used to put emphasis on "only". But in the following sentence I feel it’s the other way and it is used to put emphasis on "ever".

"Maps are only ever partial; not only are they out of date as soon as they are made, but they are also never the same scale as the territory."

Am I correct?
If yes please elaborate on the case.
Thanks in advance.