First i want to make clear my having sterbai with loaches was done without knowledge they should not be kept together; i was merely reporting my experience. There are many different species of loaches and cory and i cannot commnet on any other combinations than those i've mentioned.It can also be your setup/environment that makes them feel like their safe... Or you've gotten lucky. Some people say bettas arent good community fish (most likely cause they've had a lot of territorial or aggressive bettas). While others say their just fine for community tanks (most likely because they havent had an issue with betta aggression). So it just depends
Second there are many types of betta and some are far more aggressive than other. most people that keep betta have no clue what type they have they merely report what happens in their tank. It would be good that such reports include more specifics....