The Nordic folk have a saying."if you need a guard, you shouldn't be using a knife".
Not all sayings are always right.
If I said "If you need winter tires to drive at winter, you shouldn't be driving" - you'd tell me I'm an idiot. And I would indeed be an idiot if I told you that.
But truth is, you can drive at winter without winter tires, you just have to be extra careful (also careful about police).
Anyways, puuko knives often have round polished burl handles, and every single one I held in my hand in my life was pretty slick, and would get slippery even if just your hands are wet. Those marketed as tactical at least have rubbery handles, but I still wouldn't trust them enough to stab anything hard with them.
Considering a modern soldier is far more likely to use a knife for bushcraft than actual combat, I don't think it's a flaw at all.
Modern soldier will usually have a SAK and whatever was issued to him such as Glock knife for example.
Yet they market stuff like this as tactical knife xD
As far as the puuko, you don't see many "tactical" OTFs with a guard, either
I never saw or heard of anyone using OTF for anything at all. As far as I know people just collect them and most are safe queens.
Does a knife need a guard to slit a sentry’s throat? I like to think a lot of puukkos got put to that use in the Winter War.
I'm yet to see puukko thread without mention of winter war

But anyways, I never said you can't kill someone with a puukko and that nobody ever did it... but we would lie to deny that there are knives that are much better for that purpose.
Puuko knives are tools and also pieces of art that are to be admired in my opinion. Trying to force them into being considered as tactical knives is like telling me traditional double barrel shotgun is a millitary assault weapon...
Yeah it will kill, yeah it can be used for other stuff except combat (hunting), yeah they were used to kill people, yeah it's better than nothing in a pinch... but there's sure as hell lots of better options for that purpose.
I'm not telling this to disrespect puukko knives, they are great utility knives and arguably the most beautiful knives you can get.
But if puukko is a combat knife because it was used to kill people in war - so were kitchen knives here on balkan, and they did that job pretty well, yet we're not marketing them as something for combat...