To be comparable in size we should look at what they do. The three game engines originally mentioned have everything from physics to an entire visual IDE. A comparable smaller project is Godot not entt.
A comparable ECS implementation is what you’re after. Is entt tiny in comparison to similar projects.
Also, there is Hazel[0] which is based on entt and is the subject of an amazing youtube series[1].
IMHO, tinier means less features, at that point what could be considered comparable?