@Kaarme Smooth blades are easier to sharpen than serrated blades. And the killing power increase is negligible (since what you want to do is puncture an artery, or slash across a bunch of veins). So it's not that they ain't better at killing, it's that they end up being worse as weapons since a weapon needs to be taken care of. (And the metallurgy in the past wasn't good enough - but that bit can always be covered by magic
Sawtooth blades are better for cutting, hence why we have saws, and for a brief period during which we had good surgeons but no antibiotics, bayonets could be serrated to give worse wounds that were harder to stitch up and clean out, leading to longer recuperation periods, possibly ending with death anyway. (But this became impopular through peer pressure instead - if an opponent was caught using that kind of bayonet they'd reportedly be tortured instead of captured).
They're still in use for multi-purpose knives though, just since the saw function is useful (for other things than killing people). Usually the teeth on real examples of combined saw- and non-saw blades will be near the handle though, so you can use it more easily while cutting a line or branch or whatnot.