There's been 2 miracle tickets already btw, I guess you missed out on the first during december
Those people you're referring to... well they either have many SSRs because they whaled, or they got lucky with their jewel draws.. RNG is a big troll sometimes (to the point where one can spend 30k jewels and get absolutely no SSR, or something like a random person getting a 100% eido or core SSR hime with just a premium gacha ticket)
The next miracle ticket is probably gonna be on late july or early august
If you decided to go improve dark with that ticket, Pluto is a good kamihime to look out for, because not only does she give you great buffs (20% atk + 30% dark atk + 30% dmg cut/20% Light RST), she's also good DPS (can double/triple attack almost every turn if you have enough blocks stored, and she uses all those blocks up when she bursts to deal even larger damage)
Another one would be... Satan probably, cuz she'll get her awakening some time in August, and some people prefer using her over Amon Unleashed and she would go well with Thanatos since they have different frames for their def downs (means you wouldn't need to reorganize team in the future), plus she has orb reduction and high DATA rate i think (I don't really have her lol)
and I can't really recommend Hades since you would already be using Joan, and that's about all I can recommend for dark I think... since Chernobog nor Berith wouldn't be in 3rd miracle ticket anyway
edit: Forgot about my own queen, Osiris
Get her if you need a healer that doesn't die easily and if you want to burst early
its restricted to non limited kamihimes, and himes that were only released before it
like how Thanatos wasn't available during the 2nd MT because she was released a week later after the MT was