RNG is RNG, and the most "secure" way to get strong ssr himes is to roll the gacha as many times as possible (i myself don't believe in rate ups, never pulled those features units).

also there are not that many ssr himes that are really "garbage" there are some, but the majority are useful in one way or another. This also goes in the other direction of pulling a core hime for an element, or lets just go full crazy, get a 100% eido, which a lot of f2p players did get from random jewel/ticket draws.
Chance is always there. Is it a small chance? sure. But the gacha does not care which stuff it gives you, its a chance, it rolls the dice, everytime a new.