Samsung has sold hundreds of millions of phones with OLED screens in. Even their new entry level Galaxy J3 will have an OLED screen.
By the time the Galaxy S3 was released they had run out of OLED screens and went back to their horrific LED "Pentile" displays. So it's not like OLED worked out all that great for Samsung. Then to try to get production back up, they combined OLED with Pentile, taking a screen with lovely colors, and totally destroying it's color accuracy and eveness. Samsung has done a horrible job of keeping up with OLED demand. I'd rather take an accurate LED display, than a bright but inaccurate OLED.
To try to make up for the issue, Samsung has brought their device resolutions up to just ridiculous resolutions. 2560x1440 is ridiculous in a 5" phone, until you realize the reason they've pumped the resolution that high is to hide the issues in Pentile pixels by making them really small. But now of course you pay for that in GPU and CPU (because you have to push more pixels) and power (because you have to power the pixels and the CPU/GPU that pushes them.)
Every phone up until the S6 is still using Pentile OLEDs. That's a heck of a tradeoff to make. And Apple won't do Pentile when they do OLED displays. Samsung is throwing a lot under the bus to get OLED on their spec sheets.