I feel like this is a bit of an arbitrary and hacky solution to the problem. There are better solutions to improve Bronze experience than putting arbitrary restrictions in place, e.g.:
- Make the rental market more accessible (e.g. one-click rent from within battle screen); How many of the new players who drop out actually make any rentals? Assuming it's low, that could be one of the reasons people are leaving soon after starting. Yes, Quora is strong, but the right CL/RW/Rebellion cards can beat it in many cases.
- Give Bronze players more ghost cards (and simultaneously put an even greater RP penalty for using Ghost cards).
- Reduce rewards in Bronze (disincentivizing bots and top players from farming Bronze).
- Focus on additions rather than restrictions (e.g. Quora could be a Ghost card...).
- Push for measures that make players go up to their "appropriate" league (as Matt has been pushing for). One potential way to implement this would be to actually let players play "above" their rating, but not below it. The reason this could fix the underlying problem mentioned here is that, at higher leagues, Quora is less OP, as other cards from main sets get more abilities.