a perfect read and hit to soft or hard will still miss
Yes, very important. The speed needs to become your "constant", something you can rely upon and the factor you base you break "calculations" on. I usually try to have speed for 2 ft behind the pin, some go for 3-4ft and will have a straighter, more stable, roll at the risk of having another tricky one if missed. Too precise with distance and you might end up an inch short because the elevation indicator is rounded, it might say 1up but in reality might be almost 2. But above all - when the ball slows down it will break more so "need for luck" percentage increases when you play it very soft.
I play, or played, a lot of alt-shots in the days when you could do that without disco, and I'd say the majority of the players have problem finding the right amount of power for their putts. A Putting Pal is a good investment.