since the story behind it would fit something like that.
Ehm ... that "story" you talking about is that 4 seconds cutscene with two dialog option of wich one is certain gain and another is possible gain if you win the roll? O_o
By the time I got this Longsword + 1, it was just not special and I'm not going to likely use it.
I wonder what "better" weapon you had.
I mean, Longswords dont seem like best kind of weapons in general to me ...
Astarion have no uses for them at all, since they are not Finesse ...
Lae'zel would loose her Great Weapon fighting perk, so give her something two handed seems better ...
Shadowheart is not proficient with them ... (but her profficiencies are topic of its own ...)
As well as everyone else (i didnt check Wyll, but i have my doubts ... he tend to be played as Ranged dps anyway)
So ... feel free to corect me, but it seems to me like basicaly the only character that can use Longsword with full effectivity is Fighter Tav. O_o
And the Sussa Bark Sword also isn't all that. It's a Greatsword + 1, so I think it's good, don't get me wrong, but I was expecting some sort of special ability like "Causes Magic Disruption - Spellcasters hit by it cannot cast spells for 1 round" or something like that.
Ehm ... that is exactly what it does.

Well, technicaly it "silences" your target for 1 Round ... but that sounds just the same to me.
At least is did in last patch ... didnt check patch 6 yet to be honest.
If this effect is lost, i would dare to say BUG.

So, it's not really better than a Greataxe I can buy from the hobgoblin vendor (I think it was him) where it is a Greataxe + 1, or the Greataxe you can get earlier that does more damage if your foe is half health.
You mean this one?
https://baldursgate3.wiki.fextralife.com/Blooded+GreataxeAs it seems its not even +1 ... but that might be misstake of that Wiki, since it dont list many effects yet.
Also, the tooltip works other way around, if YOU have less than 50% then you give +1d6 damage ...
Or did you mean this one? https://baldursgate3.wiki.fextralife.com/Exterminator's+Axe
That gives extra 1d6 all the time, but only to certain creatures ...
As far as i know right now there is no plant or insect enemy (gosh i hope they dont count Spiders as Insects :-/ ) ... about small creatures, im not quite sure what that is suppose to mean honestly. :-/
And so, what I'm trying to say is that if a weapon requires a lot of work or they give it a story or make a big deal out of it, THOSE are the items that should be special. I shouldn't find Nature's Snare, for example, in a random chest in the Secret Tunnels because that is a pretty powerful staff. That should be something more like a quest reward for saving the grove or something.
Funny you mention that ...
Since aquiring this staff seems to be a little more work than to aquire that +1 Longswords ... i mean you are suppose to either search for key or sucess in two rolls (disarm and lockpick) ... that is without any doubt a more work than either win single roll (pull the sword out) or pick a dialogue choice (use your blood).
And yet in Staff case you seem to claim that amount of required work is insufficient ...
And in Sword case you talk about it like it was an hour long epic quest ...
Non-armor clothing has been sparse
Non-armor clothing is lacking in every way it even could ...
Variety of Magical Properties ... different models ... option to pair it with some other parts of gear and looking good (sory, but having a robe and Leather Gloves does NOT look good)