They are not defeated by literature, they are just not that interested in it, and therefore never practiced, and dislike working on it.
It's not a matter of the field being too difficult. It's a matter of personality.
> Quite the claim.
Yes. I've discussed this claim with people defending the opposite idea, and I've yet to find anybody making a good demonstration that philosophy is hard in itself.
They point that there is a lot to know. So reference and memory. Like most expertise in the world.
That texts are hard to read. So style, vocabulary. Well, not different than programming or the law on that point. They are easier than higher level math.
They say few people get novel ideas. Yes, creativity is rare, yet it's not particularly linked to the field. You need creativity to find new theorems too.
So they try to bring complicated topics again and again. Once we are done mapping the references, the vocabulary and cleaned out the awful style a lot of writers use to obfuscate their reasoning, the ideas behind are quite straightforward to grasp.
I've stopped doing it now, it takes a very long time, and it's always disappointing. It feels like debugging a program, only to realize it could have been 10 times shorter and easier to read.