Common sense in that the recommendations need to be taken with a grain of salt.
According to liveaquaria, your tank is overstocked and too small for your triggers and bat. They also recommend NOT putting batfish in a reef tank.
But your common sense and experience tells you that they are fine in the size tank you are housing them in and I assume your batfish hasn't eaten your corals yet.
THAT'S what I mean by "apply a little common sense"
But like I previously stated, fish usually do not reach those max sizes in captivity, most hit about 3/4 of that max size unless housed in VERY large tanks, multiple hundreds of gallons.
While a 55 gallon wouldn't be the best/ideal size for triggers, juvenile ones would do perfectly fine and if the OP is wanting a single main display fish, a trigger could fit the bill. Again, isn't the ideal size, but could be done.
If you want to be honest about it, freshwater betta's are one of the few fish that are ok with the small confines we keep them in, all other fish in the hobby would much rather be in the expanse of whatever wild environment they came from, especially marine fish.