that's not how load balancing works. load balancing is done on the server side, so you don't need mirror sites with different domain names for that... mirror sites are mainly for accessibility in case the main domain is taken down, not working properly, or to circumvent ISP/geo blocks.
Well said. Mirror links aren't related to load balancing at all and are primarily meant to help gamblers access their site in countries where the government banned the main link which is a lot better than relying on VPNs.
It's good to see more and more crypto gambling sites providing mirror links to gamblers from different countries these days reducing the requirement for VPN usage.