Depends on the fish you’re targeting. My 30# rigs and smaller are single speed and all but one is a star drag. Those will handle fish to 40-50 pounds. Fish bigger than that, I want a two speed. Sometimes you just have winch them in.
So no, you don’t NEED a two speed or lever drag, but they have their place. Assuming you’re targeting bluefin, I’d take a 30 pound rig for the little guys, and at least a 60 pound rig for the bigger models. If you can, get a 100 pound rig if the cows show up. You never know what’s below or nearby.
Yes, a 2 speed is almost a necessity for flatfall and sinker rig fishing due to the size of the fish. During the day it might not be necessary due to chasing and catching the smaller schoolie grade tuna BUT at night when they find the bigger ones down deep that are eating flatfalls and the sinker rig is when you definitely want a 2 speed. You should be using no less than 60/80 for sinker rig and 80/100 for Flatfall fishing at night. You hook a 150+ lb fish you're going to want a 2 speed. Plus I dont think they make many 60+lb reels in single speed star drag.
Using a single speed is going to be brutal on you and piss off the other passengers that have to wait longer to get going to the next batch of fish because you're using the wrong gear.