Earlier I mentioned how I would like to see the core four iconic D&D classes, and then make all subclasses as a set of occupational packages (like 5e feats on steroids). Each of the four core classes gets a class feature on the odd levels, and each occupational package gives you a feature at every even level.
Everyone loves lists. So here is how I'd probably do it, with the following packages and the prerequisites to select each of these packages (commander is like a warlord, and templar is like a witch hunter, and beserker is like a barbarian (barbarian is a background not a class

):
Occupation Package Prerequisite
abjurer INT 13, magic user
alchemist INT 13
arcane archer INT 13, fighter, rogue
arcane magic INT 13, fighter, rogue, cleric
artificer INT 13
assassin DEX 13, fighter, rogue
bard CHA 13
beast master WIS 13
beserker CON 13
bounty hunter INT 13
bushi WIS 13, fighter
commander CHA 13
conjurer INT 13, magic user
defender CON 13, fighter
divine magic WIS 13, fighter, rogue, magic user
diviner INT 13, magic user
dreamwalker WIS 13
druid WIS 13, cleric
enchanter INT 13, magic user
evoker INT 13, magic user
priest, forge WIS 13, cleric
gladiator STR 13, fighter
priest, grave WIS 13, cleric
illusionist INT 13, magic user
jester CHA 13, rogue, magic user
kensei DEX 13, fighter
knight CON 13, fighter
monk, way of the elements WIS 13, fighter, cleric
monk, way of the fist DEX 13, fighter, cleric
necromancer INT 13, magic user, cleric
ninja DEX 13, fighter, rogue
outlaw DEX 13, fighter, rogue
paladin CHA 13, fighter, cleric
pirate DEX 13, fighter, rogue
psion WIS 13
ranger WIS 13, fighter, rogue
rune magic INT 13, magic user
samurai CHA 13, fighter
scout DEX 13, fighter, rogue
shaman WIS 13, cleric
shapeshifter WIS 13
sorcerer INT 13, magic user
spirit blade INT 13
summoner INT 13, cleric, magic user
swashbuckler DEX 13, fighter, rogue
templar INT 13, fighter, cleric
totem warrior CON 13, fighter
transmuter INT 13, magic user
undead hunter WIS 13, fighter, cleric
warlock CHA 13
witch WIS 13
priest, knowledge WIS 13, cleric
priest, life WIS 13, cleric
priest, light WIS 13, cleric
priest, tempest WIS 13, cleric
priest, trickery DEX 13, cleric
priest, war STR 13, cleric
Example:
If you select a cleric class, you don't automatically get the domains. You would have to choose them. So you could choose a cleric class (and get the core spellcasting features), but instead of getting a domain, maybe you choose the bard occupational package. Essentially you would have the basic spellcasting function of a cleric,
plus additional abilities around inspiration that the bard occupation brings. Or you could choose the beserker package and have the core spellcasting of the cleric, but the rage and resistance abilities that a berserker package would give.