Short answer: The Quantity of cards in your collection not the quality of your opponent.
I'm tower rank 4 with 333 cards as of 17-3-25 (card split: 78/84/72/67/33). I'd say ~200 of those cards make ~40 playable hands that don't feel like a chore to win with as i've not levelled up a lot of my higher tier cards. 5 play cycles (~90mins each) gets me the first 17 arenas. If I were to skip all the optional arenas I could possibly claim the libido gem chest if I have sufficient free time for 8 play cycles .
I'm currently using the last arena for silver & gold farming after I collect the mythic card draw.