Nice going Jonesypunk! Thanks for sharing your experience.
Taiga makes a lot of sense with Decay. I would play more Decay main over your janky split card. I firmly believe Decay is the single best reason to play green in this deck. Especially now with Arcanist making waves in Delver decks.
4c Loam is a difficult matchup and you have to approach it like Maverick. They have plenty of hosers to contend with which include:
Chalice of the Void
Leyline of the Void
GSZ+Scavenging Ooze+KotR+Bog
PunishingGrove
WasteLoam
4c Loam is the only fair matchup where you can justify Surgical extraction if you can't deal with PFire. Surgical will also hit Loam and stop the Wastelands. You also want to bring in your solid removal for KotR, Ooze and Bob. These include your Decays, Plowshares, Paths, Pushes and Explosives. Edicts and Angrath's Rampage are weaker because they can buffer with Dryad and Mox. Grudge and Shenanigans are very good here too. A good SB tech for green builds are a couple copies of
Return to Nature. RtN is a sleeper SB card in Legacy and is better than Trophy in a lot of matchups. RtN will destroy Leyline and Chalice and exile Loam and even PFire in a pinch. If I were on green instead of white I would play 3 RtN over 3 Wear//Tear. I don't think Zombardment is good without Lingering Souls though.
As to what to take out, all your discard spells are clunky here.
Grudge is way better than Shenanigans though... The only time Shenanigans is better than Grudge is to destroy Cage. If I were on a green list I would pack 3 Decays main and 0-1 Trophy, 2-3 RtN + 1 Grudge SB. With a RtN plan you don't need to bring in your Surgicals against Loam and you are LOADED in GY hate against Lands and Reanimator so you don't need clunk like Coffin Purge. All this GY hate also compensates for the lack of exile removal. No exile or Souls means you have to pack some edict effects for Marit Lage though. That's a lot of percentage points lost on the green splash IMO.
Speaking of sleeper cards, Plague Engineer is an insane SB hoser for Legacy blacks. I expect no less than 2-3 copies in every black deck's SB as an answer to Humans, Elves, TNN, or general good Deathtouch against Eldrazi and Angler. There is very little incentive to play fringe cards like Golgari Charm, Marsh Casualties, Darkblast, Marsh Casualties or Zealous Persecution anymore.
On to unrelated news I am thinking about buying into mtgo and I would probably begin with Zombardment. I will likely update my list to reflect the modo meta and find space for some amount of removal mainboard in order not to scoop to an unanswered Arcanist. I have my eyes on a mix of Angrath's Rampage, Cratermaker, and Swords to Plowshares.
All this deck needs now is an Entomb-able Goblin Bombardment or similar free sac outlet and we'll have a chance to include 4-5 flex slots for creatures and chalices.