Shield of the Oversoul seems like a MUST in Sigarda, Host of Herons voltron. Hunting Grounds could also be of some use here. And Weathered Wayfarer is always a boss in white. Also, you need more artifact ramp like Mana Vault, Grim Monolith, Basalt Monolith, Thran Dynamo, Gilded Lotus, Selesnya Signet, etc.

Druids' Repository, Vow of Duty, Vow of Wildness, Armored Ascension, Bladed Bracers, and Blessings of Nature seem rather below the curve of most of your other stuff. My main thing would be this: is this deck voltron? Or is this deck more utility. Wolfir Avenger is good in a regular deck, but he's just a 3/3 that can regenerate in EDH and that slot in your deck can probably be used more effectively for something else.

If you wanna voltron Sigarda, some general artifact suggestions:

Darksteel Plate, because indestructible will also guard her from typical board wipes - except for Black Sun's Zenith, you'd need Melira, Sylvok Outcast for that, then you'd be just about totally uninteractive. In a creature, you could add Spearbreaker Behemoth for the same purpose. And since you have white, you could go ahead and use those wipes yourself.

Fireshrieker a cheap card to get more damage through

Whispersilk Cloak it seems almost like cheating to use it for your commander, but your opponent(s) will have to find an answer for it pretty quickly, so either it'll win you the game or you'll draw out their artifact removal.

Might I recommend Altar of Bone, Worldly Tutor, Sylvan Tutor, and Eladamri's Call.

Darksteel Plate and Shield of Kaldra are both already in the decklist. Also I've noticed that I'm strangely still in a better position than my opponents most of the time even when they board wipe (aside from when they are a "run 15 planeswalkers" control deck), my biggest issue though was when I'm dealing with other voltron type decks (specifically Rafiq conscripted) I'm hoping upping my spot removal will fix this.

Fireshrieker is probably the kind of card I'm looking for! now I wonder if it's a replacement of Inquisitor's Flail or along with for redundancy...

As for Whispersilk Cloak I have done some playtesting with it and the shroud lost me a few games. Though now that I look at gatherer Trailblazer's Boots looks like it's what I need as I have yet to see an edh deck that isn't half nonbasic mana base!

Now I'm sure if I ever acquire those creature tutors they'd probably find their way here, but I feel they'd be tutoring Stoneforge Mystic every single time.

whoops, I see now you already had Darksteel Plate. But still, I would recommend Fireshrieker over Inquisitor's Flail, one CMC more to cast, but the flail is much riskier, it makes it easier to be blocked and killed.

The shroud will only work against you on your opponents' turns, just unequip and re-equip on your turn. How did you lose games because of it?

because I'd need another creature to be able to unequip it and equipping it early kept me from being able to buff her up enough to properly race.