If classes have elements...

Based in Iruna classes, and other RPGs I've played; I would say:

Gladiator:Fire (Str is connected to Fire)

Paladin:Light/Earth (Resistant as Earth, and with some supportive skills)

Beast Knight:Earth/Fire (With good strenght and resisitance)

Assassin:Dark/Wind (Full sneak)

Sniper:Wind/Fire (Arrows fly, and they have Crossfire)

Summoner:Wind/Earth (Cause they use Nature Forces)

High Wizard:Neutral (They use different elements)

Enchanter:Neutral (Same as HW)

Necromancer:Dark/Water (Like Skyrim)

Bishop:Light (Obviously)

Monk:Wind/Earth (Fast with hard hits)

Servant:Neutral/Wind/Light (Hybrid Class)

Ninja:Fire/Wind/Dark (Fire-Wind are typical ninja elements, Dark cause they are sneaky)

Samurai:Fire/Earth/Light (Strong, resistant and fast)

Minstrel:Wind/Light (Sound travels on the air particles, and supportive skills sounds like Light to me)

Alchemist:Neutral (Alchemist are supposed to be physically and magically bad, so they use science to fight)

Fire-Str
Water-Int
Wind-Agi
Earth-Vit
Dark-Dex
Light-Crt

Alchemist: water fire dark

servant: wind neutral light ^.-

for me
hw - universal except light (unleashes blasts of the 4 elements and can use minor dark but just cant spark light even though theyre a master of major neutral magic)

alche - universal except wind/earth(uses the power of corruption to burn and poison while CURSING theyre enemies bathing on their GRIEF meanwhile staring at their BLEEDING foes as they are FROZEN in place)  

ninja - universal (master of all element and can harness the power of yin and yang)

gladiator - fire (pillar blade and blood thirst animation) wind/water(sword tempest since tempest can also mean a water slash)

bk - fire/wind (strikes like a raging fire while flashes like the wind toward their enemy and slashing them)

necro - dark (corrupted beings hehehe)

bishop - light ( do i even need to say why)

sniper - wind/ice (they make arrows rain and moves swiftly like the wind paralyzing everything on )

enchanter - all elemenet excecpt light (can manifest all the elements except light without using outside force) 

servant - wind(using their broom to blow their enemies away) light(while using the power of light to shield and create an illusion) enchanting their brooms to deal massive devastation 

assassin - dark / fire
pally - light

welp just basing on skill element (and the animation xD)

Brooms of devistation sounds like an indie band name

Adventurer: No element.

Necro: Dark/Water (obvious reasons, communing with spirits) and water, i like to think water draws a connection off the river Styx, and a possible need to manipulate it, cause it to reverse its flow (greek mythology, river that spirits must cross in order to cross to/from the underworld)

Hw: Neutral, as when you look at it, hw strongest skills are technically neutral (imp+zr) also in balance with nature and doesnt focus on one element.

Ench: wouldnt say theyre neutral, nor would i say theyve really mastered an element since their own skills are random. But for this, Neutral.

Bish: Light. Healing allies and destroying dark creatures with the blessings of almas.

Serv: Wind+Light(possibly earth). Sweeping foes like the wind and healing/shielding allies.i say earth, because how would sweeping a broom at someone blind them? Dust/dirt in the eye. Loose connection i know but im trying to think big here xD.

Monk: Wind/Water. Wind for their agility, water as they focus their mind to become calm, and cause their movements to flow, like water.

Sin: Dark. Dark for dirty fighting tactics and ability to evade detection (sucker punches and poison), was debating wind, but in actuality they arent particularly quick.

Sniper:Wind/Earth. Wind again for swift movements and Earth for their extraordinary survival skills (ailments resistances and a literal skill called survival, i know snipers have very little actual survival ability)

Summoner: Earth for their connection to nature and resilience.

Beast knight: Dark/Earth: Doesnt drinking your enemies blood to heal yourself seem a bit sadistic, or dark at the very least? On top of bleeding your enemies out and watching them suffer. Earth for their resistance to pain and keen senses (diel ancestry).

Paladin: Light/Earth. Light because theyve taken an oath to protect their fellow man and destroy darkness. Earth again for extreme toughness and strength.

Gladiator:Fire/Wind. Fire for their desire to fight as well as their strength, wind for their quickness and mobility.

Sk/Pf Ninja:Dark. Reckless, unfair fighting styles. Sacrificing lives essentially to kill someone also seems a bit dark.
Magic Ninja: Neutral. In balance with nature, doesnt seem to prefer any one tactic or skill

Samu:Light/Wind. Hear me out, samurai's were very focused on their honor, and fair fighting tactics. Honor to me screams light for some reason. Wind for their quick, precise movements.

Alchemist: Dark. Resorts to poisoning, bleeding, even burning opponents, then furthermore uses their suffering to deal a final crushing blow.

Minstrel: Wind/Water? Wind because they sing, which is essentially vibrated air. Water for their liquid voice? Really reaching with this one xD.

This was fun, never really though about what elements each class was most like.