Hey mate, I also recently came back into the game and wrote something around it as well if you are keen to have a look.

There are two ways to approach this initially, either focusing on the Chaos Legion deck or going back to the old ways as you have done. Earth splinter in the lower leagues is all magic based if the bots are using just the starter cards. Your Mylor deck will only be helpful against Fire (Tarsa) or Death (Thaddius) which seem to favour Melee a bit more.

With the low rentals, I have actually just gone and rented Yodin and some GF Chaos cards and blasted everyone to bits. Doesn't work all the time, but works well enough. Also once you are in Silver league, the FPs per win is around 1,500, so your daily chests will shoot right up.

Lastly, they don't give credits anymore as DEC has dropped so much in value, but you do still get cards which is always a plus and I did get close to 500 DEC in one chest! :)

And lastly lastly, remember to have fun!