What you describe is how you type on a manual typewriter. On which you could push a key too softly: the arm would raise, but the letter would not (or maybe just barely) hit the paper. So, you needed a firmer strike and, as you say, the strike needed to be longer. You had to keep your fingers slightly longer on the key, you had to keep pushing a little bit longer. And make sure that you applied an even pressure, to get the letters typed evenly.
This in contrast to the electric typewriter. Which basically types just like a computer: you hit the letter or not, there is no "half pushed button".
I'd say that a mechanical keyboard is like an electric typewriter. Before the switch reaches the actuation point, nothing happens; but when it does reach the actuation point it "types the letter". There are no "half way printed letters", a letter is typed yes, or no. So, a mechanical keyboard is not like a manual typewriter. The typing style you need on a mechanical keyboard (on any keyboard actually) depends on the specific characteristics of the switch: the location of the actuation point (near the top, mid way, etc.), the needed pressure, the travel to the bottom and so on.