Is it worth to play neutral Gunnthrá?

Dude, don’t give us their LvL1 stats. Use the IV Calculator and tell us their boon and bane. If you want an answer, you have to at least put that much work into it.

If you will use her Blizzard tome, Gunnthra's IVs hardly matter imho as long as you have good debuffers on her team. Lute and Arvis are great teammates with multi-stat ploys. S!Catria is another great partner with her egg and Chill res. Give her Hone Cav so she can further boost Gunnthra's offenses.

i use gunny as a great supporter. why? she gives 3 hp 4 res to any unit with wind blessing plus if used on horse emblem she can buff team with hone or fortify/ give blessing buff/ debuff enemy atk for more tanking and spd to prevent them from doubling. give her blade tome and she with other horse buffs can deal decently well. for dorcas u can always merge to another better iv one or fodder them off if u didnt invest heavily into him. and no point using units with bad ivs unless u really want to use them one way or another. if u dont care then just fodder them to make others rise

Neutral Units are almost always useable, as a general rule, they're never "bad", just never "the best". Less powerful units though, like selena, need a good IV set to work. IVs that "aren't ideal" usually won't kill a unit, and especially on someone like dorcas, the base unit can overcome the drop in stats and they'll perform their job fine. The only time a unit is truly "bad" with IVs is if they need a little extra Speed or Attack to make them good/better than someone else, and their -Spd or -Atk, something where they really needed to have as much as possible and are now missing 6-7 points. In your case, a -Spd Delthea is pretty bad (but still fixable if you invest a lot in to the spd), while Ephraim is fine with most anything since he's a buffer for the most part.