Getting back in is a bit tough, there is stiff competition in Frontier these days. To even qualify for the leaderboard you have to play 100 matches, and then compete to get more cards to upgrade the ones you have. It's a long process unless you buy some DEC to buy cards when the prices are right!
Good luck in Frontier, I don't have the cards to be competitive in Modern these days. I didn't buy any Conclave cards at all so I'm at a huge disadvantage! lol
!BBH
!PIZZA
You are right. I will buy some cards to support my progression in Frontier Format.
If you can receive key warriors from your Guild friends, it may help in your Modern format adventure.