Sure, one way to play a Paladin is as a "holier than thou jerk", but that is a fairly cliched and boring, one-dimensional character. If that is how you see them, I can understand your disdain.
And while "warrior + cleric" is fairly accurte, I find the whole to be greater than the sum of its parts.
The noble warrior who strives to better the world, fighting evil wherever it may be? The devout warrior priest who represents his deity's will? The shining beacon of Good, who leads by example? The commoner called to a higher purpose who must come to understand her inner strength in the fight to protect all from some great Evil?
I see Lawful Good, nor Paladin, as any more of a straight jacket than any other alignment or class. Must Bards always be anti-establishment anarchists? Do all Barbarians speak in a broken language and have no understanding of civilized culture? Do all warlocks have to be edge-lords?
This doesn't even get into how Paladin doesn't require a Lawful Good alignment.
It's completely fine if this isn't a character type that fits your tastes. Everyone has fun in different ways. However, I don't like your assumption that a LG Paladin cannot be fun.
The most obnoxious and fun-loving character in one campaign I ran was a Lawful Good paladin. She drank heavily, always caused collateral damage, swore like a sailor, and was a bit cracked. She also had a strict code of honor and sense of duty, always repaid any debts or damages, strove to see the good in people, and could always be relied on.
The archetype is real, but it is based on a romanticized version of the Twelve Peers of Charlemagne's court, the Knights Templar, King Arthur's Knights of the Round, and characters from other tales of valour and chivalry. No, it is not a realistic representation of history most of the time. However, it is meant to be a representation of those romanticized stories.
For me, it is simply one of many character archetypes I enjoy. The unwavering devotion to a cause is what draws me to it most of the time. Other times, I like the idea of the everyman pulled into something bigger than himself. I can't really explain exactly what makes it fun for me, it just is. But I also enjoy playing the Evil schemer, the apathetic wanderer, and the curious adventurer.