Most efficient way to rank up in arena? (F2P)

You definitely need better speed mods (speed primary arrows, speed secondary others). In terms of the arrows, it's pretty easy to farm +17-+19 speed arrow mods in mod battles, harder to come across good speed secondaries though. Empire/Sith is a good place to focus (tie fighter pilot is a good character to farm). Since you already have decent jedi it's worth noting I've seen some powerful Jedi teams with QGJ leader, JKA, Ahsoka, Yoda, Aayla, but the better ones all have a lot of speed and have a zeta on QGJ's leader ability, if not on yoda's battle meditation as well. in terms of short-term fixes, maybe put qui gonn as leader over anakin. Also gear, gear, gear.