It does make all the bats attack, but it's actually not that bad just r4 the bats when they're behind the tank and not as the tank is about to run through or in the middle of a mob. (Also with sand if you're tanking use sand as you're going away from them)
r4 Slash is a bit different from Fire Rain and Hot Foot because those are damage over time attacks and the bats will attack for every tick of damage. Which is like... 5-7 times with FR and HF. r4 Slash just hits once and boom you're good.