OLED panels don't have a backlight by the way the pixels light themselves up.
I haven't tried the A5 but Samsungs newer AMOLED screens are garbage regardless I've never seen worse PWM than on Samsungs newer panels. Even if you don't have issues like ours there's no way using a screen that's essentially a flickery mess at anything other than max brightness is actually comfortable to use (or good for you)
I assume it's because they want the screens to be as BRIGHT as possible which means the moment you start lowering it they have to massively slow the on/off cycle compared to if the screen was a lower brightness from the get go
I've seen more uniformity issues with LGs OLED but I'll take a lack of uniformity (literally the only time I've been able to see the uniformity issue on an LG is on the phone's off but charging screen where it displays mostly grey and some of the grey was a little darker) over the massive PWM from Samsung.
@Sunspark confirmed what I'm saying just a few posts up (re: v30 catching your eye - having played around on one for a while I can only see visible pwm below around 30% brightness anything higher doesn't have the signature low PWM "trail" if you move the phone. the phone still wasn't ultimately comfortable for me but much better than Samsungs recent phones since the s6 and above. Also I found it to be a fantastic phone once they drop in price I am going to get one.)