The game is an extremely long grind. Play everyday and complete your daily activities. IMO paying to progress with this account would not be a smart move as you will not increase your arena rewards for years. If you did start a new account, then it might be worth the investment to you.
Work toward other Journey Characters. Build those teams to G12 and you will do better in GAC.
Here is my main account (over 3 years playing)
https://swgoh.gg/p/196182716/
And my alt account (about a year or so with about a year off)
https://swgoh.gg/p/323533964/