Yes Marwyn and Falric were ghosts when we fought them, I really don’t know why though since they were with him in Lordaeron. Maybe he could call on them whenever and wherever if needed from the sword? Maybe the game journal would answer it.
When you use Arthas however from a standpoint for frost he doesn’t use much frost, at all. People just like to inject frost onto anything just to suit their idea. 2h frost dk on a blizzcon slide… wrong that was just generic art from wrath, no spells or anything associated with it could have been blood or unholy without a pet, could be 2h frost, could be anything really. We know what kind of frost stuff Arthas did, and Bolvar. Remorseless Winter is the biggest one. Never used howling blast as far as we know, never used frost strike, icy touch, and Bolvar didn’t use anything but remorseless winter. So from that standpoint you can play like them, 2h and remorseless winter and you are exactly like Bolvar.
I also don’t think the removal of 2h is why frost is so low on representation. Throughout my time playing I haven’t seen many 2h frost unless people just couldn’t get 2 1h weapons to drop which back then, like in Cata, I think frost was the only spec that used 2 1h weapons so they didn’t put many in the game, in wrath they had to use agi weapons and still pulled really good numbers. Legion had a good representation of frost because the artifact gave a lot of stuff that helped the spec, increased resources, increased damage like obliterate crit damage and more. All that was gone in BFA and kept a playstyle that the majority don’t like. Even if the numbers are good, the playstyle is junk and people got away from it. That’s why I did.
Now to bring back 2h would actually be simple, 2 runes combined into one fallen crusader and razorice as a 2h only runeforge, and then allow abilities to be used with 2h, of course it doesn’t address DW having more KM procs, or how DW crit mechanics work but it would bring it closer since it wouldn’t have the 15% deficit that 2h has in terms of frost damage. In wrath they were the same aside from the runeforge, KM procs and DW crit mechanics you did the same stuff just a different weapon and the playstyle was popular during that time. Or just allow a transmog which is the quickest and easiest. Why they aren’t doing it, idk. Maybe they think it would look goofy swinging a 2h sword around as fast as your main hand weapon.
In terms of fixing the spec is a different think but I have some ideas to address issues people have with the spec.