Synergies should be based on Energy and items

Honestly I think the best way to make synergies is by affinities

Fire skills synergize fire skills, cold skills synergize cold skills, melee synergize melee

If you have a skill like hydra that is fire and Projectile then it’s synergies are all fire skill and all projectile skills

That way you can use different skills from different tree and even classes

Ie: dragonscale hydra Paladin synergize with holy fire, holy bolt, vengeance, fire resist, salvation

But yeah I also though of a system where there are no synergies but the stats are boosters

Str boosts melee and fire skills

Dexterity boosts range attack, cold skills

Energy boosts lightning, magic, summon

This diversity stat distribution

Similar to that awesome MMo I played as a kid
“the 4th coming” a Diablo 1 inspired MmO where you had 5 attributes

  • endurance: determine your ability to wear armor and your life
  • str: determine your ability to use melee weapons and your damage with them
  • agility: determine you ability to use bows and your damage with them
  • intel: determine your ability to use robe, battlemage weapons, your fire/cold/lightning/necro damage, your mana
  • wisdom: determine your ability to wear robes, Paladin weapons, your light and earth damage, your buffs power and mana