When zooming out by rectangle, it's really expected that you zoom out by a ratio of the size of the drawn rectangle versus the size of the map. However, you have a fixed ratio (1.75) of the view's extent, so you may as well just have the user click a point as opposed to drawing a rectangle. Below is the code for proportionally zooming out (and centering) based on a user-drawn rectangle:
sketchViewModellZoom.on("create", async (event) => {
if (event.state === "complete") {
var extent = event.graphic.geometry.extent;
if ((extent.width > 0) && (extent.height > 0)) {
var mapExtent = view.extent;
var ratio = Math.max(mapExtent.width / extent.width, mapExtent.height / extent.height);
view.goTo(mapExtent.clone().expand(ratio).centerAt(extent.center));
}
polygonGraphicsLayerrZoom.remove(event.graphic);
}
});