I agree that this is the underlying reason why people bot:

Fundamentally the problem is that large numbers of low-value accounts out-earn fewer, high-value accounts.

I believe that one solution would be to adjust the distribution of rewards so that people with higher rating, or in higher leagues, are more rewarded. (Even more than now.)

Owning more assets means you have more cards and have them on a higher level. This gives you more options in battles and more powerful cards, and should allow you to rise higher in rating and leagues.