The set seems fine. I will do a lot of nitpicking, complaining and mediocre advice.
Okay what is the flavour and mechanics behind enchantment creatures? There are many creatures with static, triggered or activated abilities that would work as non-creature enchantments but don't have the enchantment type. Similarly their global clarity effects on both normal and enchantment creatures. Flavourfully the Ethereal ability feels like the creatures that have it should become an enchantment creature to reflect their immateriality. And finally, while all the Fables are enchantment creatures the other creature types don't have any flavour establishing the difference between enchantment creatures and normal creatures. Some spirits are enchantments, some aren't, you even have human enchantment creatures and is impossible to tell if creatures are enchantment without checking the type line.
Absolute Insight - “from nonenchantments.”
Ama, Awe of the Angelic = This a two mana white super ophidian that is immune to removal spells. The life gain draw trigger is a lot interesting without this also having lifelink. The other cards that both enable and reward lifegain and feel a bit to much like one-card combos but they’re not broken.
Calamity of Ages - This is an apparently an enchantment creature because of Clarity, yet their are many non-enchantment creature of global clarity effects.
Discrete Devotee - Why isn’t an enchantment creature? It has a static ability and really feels like an Enchantment Creature.
Featherweight Ascender - An Enchantment creature should not have the creature type human. This is a flavour fail. The same goes for all human enchantment creatures.
Holy Fire - The deal 1 damage to an innocent creature feels like a colour pie violation. Why not make this a cantrip instead?
Measure of Peace - This should not have both Scry 1 and have a Clarity ability to easily trigger the Scry 1. White is allowed card advantage/filtering by building the deck to follow a strict plan and this allows scrying without spirit tribal due to the clarity ability.
Murkshadow & Silvershadow - The colour changing ability feels mean.
Prime Serval - A seal isn’t really global enough to feel like an enchantment creature. Unless all spirits are enchantment this shouldn’t be an enchantment.
Sundown Antelope - This shouldn’t be an enchantment creature. There is no flavour reason for it and an etb effect doesn’t provide enough of a mechanical reason.
Renavowel - Similar why isn’t this an enchantment creature. If the activated ability feels like an enchantment.
Sojin the Pale - Also feels like an enchantment creature. As does Sol Grifter due to having static abilities that effect both players equal.
Sol Grifter - "As above"
Akosua - Without a static or activated ability doesn’t feel like an enchantment. Why not make it a triggered ability or give it so other cost so it feels like an enchantment.
Artisan of Whispers - “Whenever”, maybe give it the “its still an enchantment” clause like Phyrexian Metalmorph so it feels more like an enchantment creature. Also it should be a shapeshifter instead of a human
Curfew Cardinal - Could be an enchantment creature. Same for Dream Dismisser.
Divergence - This effect is more red. Blue has gotten this card without the attacking clause to show its more defensive. Colour pie bleed.
Enthrall - Cool design.
Jinxed Elemental - This looks overpowered. It also should be a Sorcery.
Overwhelming Wisdom - This looks overpowered. Either bump up the cost to three or stop it being an instant. It also enables draw go counter-spells far to easily. (This seems to be on the same power level as Accumulated Knowledge and Squadron Hawk)
Stormsurge Leviathan - This attacks each turn if able and super menace should be seperate sentences.
Temporal Assailant - Is probably easier on the rules if instead of changing the order of phases does something like “Permanent untap during each players end step instead of during their untap step?”. I unfortunately don’t know enough about the rules to know how to change this.
Essence Hoarder - Chould the effects be merged into “Exile a spirit card from your graveyard until Essence Hoarder leaves the battlefield”.
Feed on the Damned - Since the creature is already going to die does this need the “When that creature dies this turn” text.
Gravegorder - This a bomb. 5 mana for all three zombies would be fine but this gives you a 3/3 body as well. 9 power for five mana is too much. At least bomb the life-loss up to 2 per zombie or something.
Haunting Banshee = Maybe, “whenever a creature would die, exile it instead.”
Insatiable Appetite - Again feels like an enchantment creature.
Tyrant of the Meek - could be an enchantment creature.
Belligerent Solicitor - could be enchantment creature.
Cinderflinger - Why basic land in particular instead of land or mountain?
Delude Timer - Maybe “Take an extra after this one. At the end of that turn, skip your next turn.”
Flame Warden - I don’t think this is worded correctly. Probably “Whenever a spell you control would damage to a creature or player, instead it deals that much damage plus one.”
Give in to the Flames - The amount of damage should be five instead of six. Red get five damage for five mana but usual needs extra mana to do six damage.
Imps Breath - You should choose the target before you roll the dice. You could reform the choices as a modal spell.
Lightning Howler - Considering the cost you make it exile cards equal to the damage dealt instead of a replacement effect.
Shy Reflect - According to gather I think it should be worded “Change a single target of target spell” (using Sideswipe)
Spellweaver’s Embrace - This is interesting enough as an aura that gives you the boost without Clarity. The drawback of your opponent getting the creature back with the aura boost should make it acceptable at 3 without the clarity effect.
Stumble-Fumble Pilgrim - This might work in the rules but its an awesome design. Besides the effect is blue and not red. (Future Sight).
Vicious Firecat - This creature is far too cheap for a 1 power double striker. Red normally gets 1 power double strikers for two mana at the absolute minum. Also as its an enchantment it should negate all damage prevention instead of just its owners.
Bellowing Jungleworm - The triggers should be merged “exile a land card until Bellowing Jungleworm leaves the battlefield”.
Harmony’s Patron: Due to the existence of enchantments with discard costs this card could be an enchantment.
Read the Leaves - The sacrifice effect is a colour pie break as it allows card draw without creatures. Also why ‘basic land?”
Scattered Creeper - This only effects itself so why is it an enchantment creature? The creature below it, Scatterseeed Oak, at least has a clarity ability that effects you universally.
Treetop Dweller - A spirit with an activated ability that effects the board Universally. Why isn’t this an enchantment creature?
PS: Can I burrow the term Etherial for a variant mechanic?(Can't be blocked except by enchanted or enchantment creatures.)