Does your chain saw only last three or four sharpenings?
What's a better chainsaw file than: Oregon #23727 3/16" (4.8mm) round file

SITUATION:
A few months ago, I bought a new Husqvarna 445 18" chainsaw.
I bought, at the time, two Oregon #23728 round 3/16" (4.8mm) chain saw
files (in addition to a depth gage and flat file). After only about three
or four filings, I noticed the file slipping more easily (and not biting).

Switching to the unused file (they came in a 2 pack), I noticed the unused
file bit much more than the now-used file.

TECHNIQUE:
There are only 36 teeth (18 each side) on the chain; and (with a new file),
it takes only four to seven swipes per tooth to sharpen.
It seems to me that a chain saw file should be HARDER than the chain saw
teeth, and that it should outlast the chain. Certainly it should, IMHO, get
a few dozen chain sharpenings.

MY QUESTION:
Q: Do you only get three or four sharpenings per file?
Q: If you get more, where can I get the 'better' chainsaw file that you
use?