Of the three elves we've met so far (there might be one or two other minor ones in flashbacks) only Kraft can be said to have changed class (warrior to monk), and that was centuries before the time of the series at the earliest, and due to a crisis of faith (and possibly a midlife crisis, or the elven equivalent of one).

The other two have spent at least a thousand years focusing on very specific skillsets (and in Serie's case complaining about how humans don't live long enough to gain proper expertise at their crafts)...

The premise of the series is Frieren learning to appreciate her friends despite their short lives (well, the original premise was a cute immortal terrifying demon killing machine of an elf, according to the author, but it sort of evolved from that)... but when it comes to the nature of elves and how they learn, it's pretty much the absolute opposite of this.

Both Frieren and Serie would be extremely offended at the mere suggestion that they might possibly ever forget anything, and Kraft would probably be disappointed but understanding.