Joining a guild is a good thing for new players and should be encouraged because it builds relationships and grows the community. Throwing a nerf bomb at the gladiator system undermines the value of joining a guild.
Summoner cards like Yodin, Kitty and LLama have been even more dominant in battle than Gladiators and priced out of reach for many new payers to own but there has never been an uprising to suggest they are not suitable for bronze play.
There are other ways to tackle the dominance of overpowered cards such as introducing new cards that are more affective against them or by allowing them to be traded or by just using the existing cards that can (stun, dispel, half, cripple or afflict) in more cunning ways.