There is a priority for event girls implemented. They are 3x more likely to drop with regards to the other girls. But yeah, priority doesn't mean guaranteed, so sometimes you will get one of the other girls instead.

About the 10x epic pachinko being overprized: for you it maybe is overprized, but if they didn't make a fair amount of money from it, they would've changed it already. So clearly there are enough players to actually buy the kobans for the dev team to say this is the system they will use. Remember that you are getting kobans for free in the game, and that you can actually do a 10x game every 2 to 3 events if you really want to without paying anything.

Off course you can always suggest some changes, but in my eyes the changes you suggested will just transform the game into every other game on nutaku. There are enough of those games out there already.

at op: yes you can get regular girls during events as well. you can either call it bad luck or good luck depending on how the rest of the event unfolds for you. If you happen to get Kalissa as well, you will have 2 girls instead of 1, which is good luck. If you don't get her, then you could call it bad luck. Message is; go on battling Dark Lord and she might eventually drop.