There is no question that Live Arena can be a Royal PITA, but I am pushing 20K in G4 and I use mostly fusions, event toons & reward legos with a few others thrown in. You can absolutely fight & win with accesible toons.
Here are my go-to toons:
Marius (Always my first pick if I have the choice)
Padraig (Got him from the Hero's Path)
Arbais (But my Arbiter is actually faster and could easily be used instead)
Shazar (I like Gnishak better as a Bomber, but Shazar has that sweet speed aura)
Fabian
Gnishak (I go double bomb squad against Kommidus, Nais, Galathir, Theodosia....because well built 5/6 star awakened Mythical Tanks can't always be killed by one bomber alone)
Kharnage
Embrys
Occasionally WuKong or Pythion
Depending on circumstances, I do occassionally use Nick/Noelle, both of whom were avaialble last Christmas.
I haven't built Hilvi yet, but whenever I get around to it, I will then have Tormin/Hilvi (AKA GirlTormin) as an option. They were also both avaialable through in-game events. Everyone and their brothers, sisters & cousins has Hilvi built in 9 pcs Mercurial, so I am sure I won't do that.
Armanz is no longer what he was 2 yrs ago, but he is still very much Meta.
Freyja was avaialble from a DoF, and if she is built well, she can be used like a Siphi.