It was nice of the ST to offer a special black and white screen mode on a custom monitor. The Amiga had the memory bandwidth to offer the same, but chose to only offer PAL/NTSC and no other custom video signals at launch, probably to avoid making its display chip even more complicated.

The Amiga had a "professional" resolution of 1008x1024 PAL or 1008x800 NTSC, 4-colour greyscale with a 15Hz refresh rate via its A2024 monitor (which effectively sampled 4 screens worth of video output and stitched them together).

You could also buy a "flicker fixer" (later included internally in the A3000) which gave you full colour 640x512 at 25Hz or 640x400 at 30Hz if you didn't like interlace.

In 1990, the ECS chipset gave you "Productivity" mode (640x480 at 60Hz, 4 colours) and "Euro72" (640×400 at 70Hz, 4 colours) - there's a nice list here: https://amiga.lychesis.net/articles/ScreenModes.html

But different strokes for different folks. The Amiga distinguished itself by being easily genlockable to video and having a 4096 colour palette and 21kHz 4-channel 8-bit sampled sound replay in 1985. The ST distinguished itself by having MIDI ports and a choice of either monochrome monitor, or the TV (or a colour monitor based on NTSC/PAL) if you wanted to do anything in colour. It found its niche in controlling other musical devices.

But the ST did have a garish green low-res desktop by default.

Later Amigas also supported VGA monitors with 31kHz horizontal refresh rate, with just a passive adaptor. I used a VGA monitor with my Amiga 1200 up until I switched to PC, and a tweaked video mode with 704×520 pixels.

If you wanted to play games on an Amiga or an Atari ST you needed to use a TV-signal compatible 15kHz monitor or a Multisync monitor. I ran desktop programs in 640×200 mode with four colours on both my ST and my Amiga 500 before I upgraded.

There were also "flicker fixer" add-ons for the Amiga, converting the interlaced modes to VGA signals: one was built into the Amiga 3000.

As a kid the 70 Hz made a much more professional impression on me than the colors, but of course the colors were much cooler.