Both the anime and the manga are fantastic.

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.

Elves can live over a thousand years (one dark elf we know of is blessed by their evil deity and is over 5,000), but dwarves only about 2-400 years (I think?) and half lings about 100-150ish, humans standard 80.

After reading The Age of Em (2016) by Robin Hanson, I wish there were stories about races that went the other way, lifespan-wise: extremely small people who lived only 1 year, even smaller people who lived only 1 month, some very extremely small but very powerful ones that lived only a day, etc. The idea is that artificial people (emulated people, or Ems) could have subjectively similar characteristics and experiences to the larger physical entities (e.g. humans, but perhaps even dwarves, elves, and etc., since theyʼre just emulated minds), but their artificial emulated substrate allows their minds to develop and age orders of magnitude faster; they also could solve certain problems orders of magnitude faster but practical limitations on delays between thought and physical interactions (your mind would waste away if you had to wait a whole subjective hour between each physical step during a walk with a standard 1.5 meter body) require their bodies to be very small.

To ems that are smaller and faster, sunlight seems dimmer and shows more noticeable diffraction patterns. Magnets, waveguides, and electrostatic motors are less useful. Surface tension makes it harder to escape from water. Friction is more often an obstacle, lubrication is harder to achieve, and random thermal disruptions to the speed of objects become more noticeable. It becomes easier to dissipate excess body heat, but harder to insulate against nearby heat or cold (Haldane 1926; Drexler 1992).

A crude calculation using a simple conservative nano-computer design suggests that a matching faster-em brain might plausibly fit inside an android body 256 times smaller and faster than an ordinary human body (Hanson 1995).

Compared with ordinary humans, to a fast em with a small body the Earth seems much larger, and takes much longer to travel around. To a kilo-em, for example, the Earth’s surface area seems a million times larger, a subway ride that takes 15 minutes in real time takes 10 subjective days, an 8-hour plane ride takes a subjective year, and a 1-month flight to Mars takes a subjective century. Sending a radio signal to the planet Saturn and back takes a subjective 4 months. Even super-sonic missiles seem slow. However, over modest distances lasers and directed energy weapons continue to seem very fast to a kilo-em.

Call them speedlings, or some variant of sprite, but I think its an interesting world-building concept.

I feel like that campaign is just begging for Lolth to show up and just be like "I see you've done... well for yourself. Are you going to introduce me to your new friends or...?"