The screen doesn't really have strong limitation and can run at 50Hz. Technically the screen can go even higher than 50Hz for partial screen refresh.
It is however very difficult to compare the Playdate with the consoles you mentioned because the Playdate doesn't have special hardware to handle rendering. Consoles like the SNES, GBA or genesis are specialised to display tilemap and sprite on the hardware level, they technically do not have framebuffers. Consoles like the DS or PS1 have a frame buffer but with some GPU that can render polygons and sprite in the frame buffer in parallel to the CPU (The DS is even more complicated than that, but that's a different story).
On the Playdate all the rendering is done on the CPU. The SDK provides a sprite system that makes sure to render only part of the screen that will change and prevent overdraw. So even if the CPU is way more powerful than any of the consoles you mentioned, it has to handle much more, rendering, audio, etc.
The advantage is that you are not forced to use the sprite engine from the SDK and come up with your own rendering adapted to your specific game. Though it has to be said that this sprite system from the SDK is very well optimised and very versatile.
The general bottleneck is simply how much has to be rendered. So how much of the screen has to be redraw during each frame (you can see that in the Simulator with the option Highlight Screen Update) and how many sprites has to be tracked and how big they are.