Avoiding the Theme Park Version of Buddhism

Basically, how do I not get boxed in with "being faithful to the source material" when incorporating Buddhist and East-Asian mythology into my story? Obviously a breathtaking Space Opera starts to lose a bit of its luster when, say, the plucky space pirates end the story all learning a lesson about the futility of materialism and all the Space Marines are nonviolent ascetic monks (yes I am aware there were actual Buddhist warrior monks and yes I know they could be extremely violent). So how do I retain my creative license without doing disservice to the actual religions and mythologies I'm borrowing from?

Don't think of their religion as the defining aspect of their character. Write them the same way you would anybody else, with the same range of personalities and motivations, then impose their religious values on top of those preexisting personas. In short, create characters, and use their faith as flavouring.

We have several Buddhist tropers here, including Aondeug, so you may try PM'ing them and politely asking for advice.

...not Buddhist, but I nonetheless take serious issue with the idea of religion as "flavouring".

This.

Yeah, using beliefs as a character's 'flavouring' does kinda sound like purposefully adapting Theme Park versions of it. For creative and diverse aspects of a belief, though, you can always take in other factors such as sects and denominations.
Or, in the opposite direction, not emphasizing beliefs may actually avoid Theme Parks. As I understand it, Theme Park versions occur when you exaggerate certain aspects beyond what its real-life practitioners practice, right? I mean, most Buddhists around me just casually adopt non-avarice, just like most Christians around me just casually go to church on Sundays.
Then again, this advice probably doesn't work when writing a fundamental beliver or an actual clergy member. In that case, well... doing the heavy research is probably the only answer.

The key is to write multiple characters with the same faith who are nevertheless very different. I have a Muslum protagonist who forgets which prayers are spoken out loud in a key scene, and another who could never forget something like that.