Is the premium summon rate really 50/50 chance for non silver unit on the Nutaku version?

I've drawn over 15 units so far and I've only had a single gold unit out of it, everything else was silver.

At this rate, 5$ per silver unit, it's really not worth spending any more money on this game, it really doesn't look like it's 50/50. I'm not saying thin-foil hat/it's rigged, just that maybe the rates are different than those on DMM? The wiki states the rates, but there is no source stated.

Or maybe it's weighted towards the more SC you have, the higher your chance is?

Or am I pressing the wrong button? I'm using the "Summon Premium Unit, 5 Sacred Crystal". Am I supposed to use the "Summon Rare Unit, 3 Sacred Crystals"?