You can totally do 2k dimming zones in a 27" panel. The Macbook Pro has 2500 dimming zones in a 16" laptop panel (they advertise 10,000 LEDs, but those are 2x2 per zone). That's over triple the zone density of what 2k zones at 27" would be.
Increasing zone density has diminishing returns though and fails to solve the biggest downsides of mini-LED. High-detail/high-contrast elements like text and ui elements, or starry skies, fireworks, etc, in media content, are gonna be almost at bad at 10k zones as they are at 1k zones. The only way to make those look good is with per-pixel dimming.