Indeed. I agree with Neko - when i go up the levels i have Trophy Chance really rare - usually one time per severall stages/rerolls if failed on Choice of Fate, and i get mostly 5/10 or even 0 trophy cards from it. 30 or 50 is a big luck, while i barely saw 300s more than once per Phase 1 and 2 until getting to Bonus Stage and 100s more than once a day (saw, among the others - not picked them). While on the Bonus Stage i get Trophy Times like on every 3rd roll, and they mostly have 4/6 silver cards (30/50) and 100s very often, and i sometimes even catch 300s even without Radars. It also has alot of Boss fights, which means alot of silver and some gold keys and alot of corresponding cases. While Radars are most useful on normal stages, to keep the Trophy Chance and Boss Encounters at a decent rate. But my biggest mistake is, probably, the fact that i save Radars until i complete my Daily Missions. (since they prevent me from getting triplets of Exp and Pero for reward SR WCs for 18 of the same kind per day). Guess i've found what's messing up my 50k achievement.
Also, as mentioned before - when you lose on Choice of Fate you get "Consolation rewards" instead of "Advancement rewards" - which are much less valuable, and lose extra STA to go through the same area again and again - while STA cost and number of rolls to get to the Choice of Fate is different on different stages - so, sometimes, it's just a watse of extra STA, "running on one place", like a threadmill - you exhaust your resources, but not moving forward. Of course, sometimes i get the correct card on Choice of Fate even if there was only 2 or even 1 correct cards from the first or second try, but sometimes i get really stuck on one stage for like 10 tries/re-rolls! I don't think it is worthy to replay one stage so many times. Without glasses on 1 correct answer times i could easily fail to unlock all story chapters during last 2 Gambits, seriously. And i don't wat that for sure. Even more than losing that 50k card (i can still view the card on the Wiki later, but there is no way to watch/read the Gambit storyline outside of the game yet).
My other mistake is that i used to waste all the glasses/radars at the end of Gambits (even fed them to Kurito without other pricy items to get special cards) because i thought they vanish like Shakes/Burgers on Event's end. I guess that's why i lost the last two 50k cards.