Those spines are for protecting itself from becoming food. I.E. something like a huge grouper swallowing them whole. Additionally, you only get stung from the end of the fin. Smaller, more nimble fish usually just nip the fins of the lion in half.
Also, I'd say an adult Volitian Lionfish is too big for a 135, they can be over 15" wide so I'd only house them in a 2' deep tank. And the porcupine puffer will definitely outgrow a 135.
IMO, the porcupine puffer will be worse on the lion then a lot of triggers...