legacy chain?
what does that even mean.
What is a valid fork with the same history sine before August 1st?
who decides?
The market decides. I think it's pretty clear the market wants to stay on the chain with the most competent developers working on it, which is clearly Core right now. Bcash is a disaster with its EDA mess which also shows you need competent devs who properly test and peer review the code. B2X for the same reason will become just another altcoin. I'm not getting into any conspiracy theories here, they are very boring and uninteresting.
It is always about the developers first, and the community. The chains with the greatest agregation of development talent will have the best and most relevant tools and software. Community and distribution are important, but they tend to grow from the development ecosystem.
The effective airdrop in BCash provides a starting distribution, but it is only a snapshot, and will be siphoned away slowly by the gravity of the system with the greater mass.
The conclusion is that Core is the winner. Relative price movement will confirm that, as it is doing right now.