As someone who thinks class story is more important to creating a character than class mechanics... I wholeheartedly support any class design that includes its own narrative and reason for being. Which basically means I think multiclassing is lame. Multiclassing to me is usually just caring about combining a bunch of game mechanics together, with little to no concern of the character's narrative, background or story that would illustrate the reason for that combination of multiple classes.
The Paladin class has a story. A reason why it exists and what the character wants and needs and hopes to achieve by being a Paladin. So a player who takes that class has a design for their character along the path of that story. Whereas a Fighter/Cleric does not have that kind of narrative more often than not (unless the player chooses to create one.) I believe that usually a player makes that multiclassing choice not because they have a story for their character they want to play out (since if they merely cared about playing a warrior with a religious bent they could be just as happy playing a single-classed Fighter with the Acolyte background)... but because they want to use some Fighter mechanics alongside some Cleric mechanics.
In my opinion this is especially true with regards to the four Charisma classes-- people have been multiclassing Bards, Paladins, Sorcerers, and Warlocks with each other for the past 10 years usually not because they care about the story and background of someone who combines the very specific narrative details of those classes together... but because their mechanics all just synergize really well. Few people make a Bard/Warlock multiclass because they have this narrative idea for a character who was a bardic college graduate that found some dusty tome in some strange library and who read it and ended up making a deal with some extradimensional entity and seeing how that dichotomy played out in the character over the lifetime of the campaign (for example)... but rather because the player said "Hey! I can play a Bard who can fight using my Charisma stat for attack and damage if I multiclass Hexblade!" And that was the entire reason for multiclassing. They just wanted the mechanic to make their bard fight better.
And that's fine if that's what some players want-- I'm good with the game including multiclassing rules so that those players can have that at their fingertips. But I'm also incredibly glad the game doesn't have just that, but instead gives the rest of us additional classes as well that presents us with narrative design in the class's core. Some people might love the idea of just having the Core Four and then relying on multiclassing to create all the other archetypes... but I'm not one of those people and I'm happy to know the WotC designers do not appear to be that either.
The Paladin class has a story. A reason why it exists and what the character wants and needs and hopes to achieve by being a Paladin. So a player who takes that class has a design for their character along the path of that story. Whereas a Fighter/Cleric does not have that kind of narrative more often than not (unless the player chooses to create one.) I believe that usually a player makes that multiclassing choice not because they have a story for their character they want to play out (since if they merely cared about playing a warrior with a religious bent they could be just as happy playing a single-classed Fighter with the Acolyte background)... but because they want to use some Fighter mechanics alongside some Cleric mechanics.
In my opinion this is especially true with regards to the four Charisma classes-- people have been multiclassing Bards, Paladins, Sorcerers, and Warlocks with each other for the past 10 years usually not because they care about the story and background of someone who combines the very specific narrative details of those classes together... but because their mechanics all just synergize really well. Few people make a Bard/Warlock multiclass because they have this narrative idea for a character who was a bardic college graduate that found some dusty tome in some strange library and who read it and ended up making a deal with some extradimensional entity and seeing how that dichotomy played out in the character over the lifetime of the campaign (for example)... but rather because the player said "Hey! I can play a Bard who can fight using my Charisma stat for attack and damage if I multiclass Hexblade!" And that was the entire reason for multiclassing. They just wanted the mechanic to make their bard fight better.
And that's fine if that's what some players want-- I'm good with the game including multiclassing rules so that those players can have that at their fingertips. But I'm also incredibly glad the game doesn't have just that, but instead gives the rest of us additional classes as well that presents us with narrative design in the class's core. Some people might love the idea of just having the Core Four and then relying on multiclassing to create all the other archetypes... but I'm not one of those people and I'm happy to know the WotC designers do not appear to be that either.