Are high tier items used in PvP? How hard/time consuming is it to make top tier weapon?
Depends, you only need to craft Superstims and maybe drugs and ammo, rest is farmable (avengers, gatlings, sniper/laser/plasma rifles, zookas, lsw, m60).
One person can do this alone by using sandboxie taxi + fighter in TB, mostly you lose nothing, sometimes some ss and ammo (on NCR army you practically lose nothing if you use m60 and looted ammo/guns).
For a player that know's how to get stuff, crafting is HARDER than farming, because it's more time consuming and you've got bigger chance to meet other players that just want to take your new shiny things.
Items in fonline, especially crafted aren't efficient, because you can die easily by encounter/bug/connection drop/bluesuit/anything, and you'll lose it, and after lost of farmed item you won;t cry so much.
Crafting also is boring and needs alts, even harder to lvl up than fighter ones (to enter sierra you need sniper and to craft you need crafter, if you want to make hybrid, then you need other ccrafter alts for other professions, instead I prefer going to NCR army/unity which is more fun and you learn some tactics etc, by crafting you learn nothing but patience).
If you talk about TLAmk2 I can answer too, my friends from SQ play there, they got one chracter for crafting everything, walking around etc. and their fighter alts use looted weapons but crafted armors for PVP.
Stuff is way easier to get there even than on 2238.