Which is more important: preserving the lore of a setting or having the full range of PC character creation options?
For example, in the lore of Dragonlance between the Cataclysm and the start of the first novel there are no true clerics. Likewise, there are no halflings, orcs, changelings, tieflings, dragonborn, etc.
So which is more important: preserving existing lore or the full range of 5E PC character creation options?
The way that the question is asked may be biasing your results.
I do not break my lore - in terms of changing it to create a contradiction with something established. HOWEVER, I do
add to my lore, including making exceptions to rules that may be thought to be absolute, but perhaps were not in reality. If I set a game in Krynn set between the Catacalysm and the first novel and a player wanted to play a dragonborn cleric of Paladine, I would look for a way to make it happen. I'd talk with the player about their ideas. I'd get creative. While doing so, I'd want to establish: 1.) Why doesn't anyone know of the race, class and situation when the first novels roll around? 2.) Why is this unique race present? 3.) How does the presence of the PC impact the lore? I might work with the player and suggest that the cleric be a traveling PC from another world that worships Bahamut and is there because they'd discovered that Paladine, who they think may be another name for Bahamut, left these people and wanted to bridge that gap. Then I might have them be folded into the lore as to what inspired the Draconians.
This is not choosing between lore and player options - it is melding them. It is developing them.
Now, if I'd had an event take place that established, beyond a reasonable doubt, that no cleric of Paladine/Bahamut, from Krynn or elsewhere, had been in Krynn at this time, this option would not be on the table as described. However, I rarely find situations where you can't enhance the lore to account for a player option and maintian the integrity of the lore. In fact, I can only recall one situation, and it was toughy because the absolute rule that was being violated was something that had been hinted at to the PCs, b ut they had not confirmed - but major storylines turned on the issue. By denying it, I was giving a hint to them that spoiled a discovery yet to be made.