Throw the "patching plaster" away.
It is a horrible product not really suitable for much of anything.

Old finish plaster was a mix of lime putty and gauging plaster. Setting joint compounds are a modern version.

You can skim the surface with Easysand and the work will go much faster with a plasterer's trowel instead of drywall knives.

You want a trowel with a decent handle diameter, like at least 1.5 to 2 inches.

The little 3/4 inch round handles are not worth working with.

When you use the trowel to spread over a large area you rotate your hand slightly to raise the edge of the trowel in the direction of movement.

The trailing edge leaves the surface with a smooth finish.
When you sweep back in the other direction, rotate the trowel to raise the leading edge.

I only do large areas a few times a year and it still takes some time to get back into the correct movements and rhythm of sweeping back and forth to spread the plaster smoothly.

Start in a less visible area like behind a door, or in the wall adjacent to the room entrance.