Originality isn't the main issue - as long as you aren't straight up ripping off a pre-existing story and just doing cosmetic tricks to cover it up.
The main issue is telling it well. Even something as old and tired as the farmboy who is secretly the heir to the throne (the oldest trick in the book of high fantasy clichés) can be interesting if it's done well. If you manage to make your farmboy-prince someone who is interesting, and who has depth, and who is a person rather than a collection of stock traits.
The same goes for worldbuilding and plots and conflicts. So your farmboy-prince is threatened by some evil force who for some reason doesn't want him on the throne, so he has to fight it. These are all stock plot-devices, and if you present them as such, of course it's going to be boring - so take those stock things and do something with them! Maybe the evil force that doesn't want him on the throne isn't literally evil - what if they're just an opposing force? Like instead of it being a moustache-twirling servant of an evil god, or a prophecy foretelling the end of tyranny or whatever - maybe it's an advisor to the previous monarch (your farmboy-prince's dead dad), and that advisor is convinced your farmboy-prince would be a terrible ruler, because, well, his dad was kind of a terrible person who did a lot of damage to the kingdom's economy.
That's just one tweak, and we've already got a more interesting story - even if we're starting out with the same basic building blocks.
Think of it like this - a really great chef can make an amazing meal out of the most humble ingredients. A bad chef can't make a good meal even if they have the best ingredients in the world.
Also, to add to @Kamikaze's point about GRRM borrowing from real world history for GoT - seriously, if you're doing any kind of high fantasy and/or political plot, do yourself a favour and read up on history. You will not BELIEVE what people have been getting up to in the real world.
Like, don't even get me started on that one time a crossdressing possibly trans* Syrian 14 year-old who was convinced he was the literal incarnation of a mystical sun god ended up ruling the Roman Empire for 4 years. Which is a thing that really happened, in the real world.
*) I write "possibly trans", as the whole trans-identity was not a concept that had been invented at the time, and also the historical record isn't always reliable, and that bit might well have been made up.