Heh, larger claws doesn't always mean more aggressive.
I've bred and kept Neon Red crayfish/lobsters (max around 5") with a tank full of fish (corydoras and tons of guppies) and they wouldn't really actively hunt any of the fish. Sure they would challenge the corys by raising their claws and walking slowly towards them to move them out of their way, and yes occasionally I would see a cut tail fin, but they never hunted any fish. The corys could even be seen right next to the crayfish without being harmed. Guppies could also swim by the crayfish just fine, well at least most of the time, sometimes it seems the crayfish can get rather bored or just feel like picking on something and will sometimes lift their claws up waiting for a guppy to swim by. Only seen a couple guppy tail fins damaged, but that was it. Through the about, 2 year time span that I have kept them all together, there was only a few instances of deaths, I've only had 1 dead cory and maybe 3 young guppies (not all at once). So those death instances were rare and so they definitely did not hunt. And this was a non-planted tank, just gravel and a few decorations (early days...) and the tank was pretty packed full of fish and crayfish so the little room there was, if they were hunters all the fish surely would have been caught easily and all the fish decimated. Despite the infrequent fin "pinchings", none of the fish lived in fear of the crayfish (they would go right by the crayfish). They would still raise their claws up at me/people, fish nets and gravel vac tubes, like commonly seen among large clawed inverts haha. Never been pinched by one
Oh yeah, and I did house some of the adult crayfish in my larger tank with giant plecos, clown loaches and a arowana and they definitely didn't mess with those bigger guys.
Haven't had any of those clawed dwarf prawns/shrimp like you have had, but it sure does sound like the species you have is quite the aggressive hunter, even attacking larger sized fish (so I've read, if it is a Macrobrachium sp.).
Not doubting your experience with these inverts, but just mentioning mine as a note that larger claws don't necessarily mean more aggressive. I haven't kept any other crawfish so they very well might be more aggressive than the species I had.
Oh yeah, the crayfish did fight with each other (natural behavior, territorial and mating rights), but got along most of the time.
But awww. Poor endlers if they have to live in fear/danger of getting killed by the prawn...
would look at housing it alone (even if you have "too many" endlers) or with larger fish that won't be in danger.