Terrible idea... these cards are only unlocked by playing in and doing well in a ton of brawls. Any new player in any league will have issues. Can't rent a Gold deck and get these, you will still be missing them. Either unlock them, or leave them for all to play. Otherwise you are giving literally useless brawl rewards to players who buy and build their decks to play in bronze.
Legendary summoners are worse for new players. I lost so many matches when I came back to Kron, Lamma, and Yodin that I could not afford to buy, and renting was impossible at times, but they got phased out and the playing field leveled.
It would be better to tie these to a set, and phase them out like the promo and old reward cards. Moved out of modern and into Wild, release new Gladius cards.