If I want a softer volume, my fingers fall more slowly with less force
No - this is what you want to avoid lol
I'll explain why.
But first I have an exercise for you

Sit on a chair, place your arms on your legs and relax them completely. Get someone to lift one of your arms just above the wrist joint. DO NOT help them at all i.e. the full weight of your arm should be in their hand. But don't push down, as this is you 'trying' to make your arm heavy. Try also to avoid the tendency to 'help out' when the person lifts your arm. If you do this, your arm will go 'weightless' in their hand. Relax everything absolutely and completely, as in a puppet on a string. Btw this is very difficult to do - to 'switch off' your brain like this.
Make sure you are relaxed at the shoulder - don't pull the shoulder up when the person lifts your hand. Don't push the elbow out either. Also - if you are completely relaxed, your hand will 'flop' at the wrist. PS if you are fully relaxed you won't need to think of any of what I have written in this paragraph, but what I have mentioned are common things that people do when they think they are relaxed.
Imagine if someone chopped your arm off and handed it to you (aside from the pain lol) - it would be heavier than what you expected. Look at your lower arm - it is actually quite a large mass of bone and muscle. It is really difficult to be aware of the actual weight of certain parts of our bodies, since we are all used to holding ourselves in certain ways. Our muscles compensate for the weight.
OK - next step - this is very difficult btw - try to lift your
own arm. If you are right-handed, begin by using your right hand to lift your left hand, then try lifting your right hand using your left hand. It is very very difficult to do this to begin with. It is tricky to switch half of your body off whilst the other half is 'active'. PS this will be impossible if you can't relax when someone is helping you out. That should be second nature nefore you try what I just suggested.
OK now back to the piano lol. You shouldn't 'try' to play soft - this will just produce a weak tone. For now anyway, if you want a lot of volume, lift the hand high above the keys, and let gravity do the work i.e. let it fall onto the keys. don't worry about what notes you strike. The main thing is to develop the sense of freedom in the movement. Make sure your fingers don't tense up and try to strike the keys when you come down.
If you want to play soft, your fingers should fall from just above the key, rather than high above the key. But the weight should be the same i.e. gravity should do the work, rather than you 'trying' to play at a specific volume. If you 'try' to play at a specific volume, you'll probably find that the control you have over the volume is inconsistent.
So - remember - don't try to play loud or soft - judge it by the distance you are from the keys. Let gravity do the work. You'll eventually work out at what height from the keys your fingers need to be in order to play at specific volume levels.
(You said your fingers 'should fall more slowly' - don't try to control the speed - learn to let go. Also don't try to control the force - gravity will do everything for you. If you try to control the way you are doing, the sound will be 'brittle', and when you get to playing difficult pieces, you will tire very very quickly.)
I hope you can see how this relates to the relaxation exercise - it's almost the same thing you are doing.
PS don't worry about when you have to play legato and control volume i.e. playing scales - deal with the previous exercise first, and then we will get to that.
PPS this is 'Russian School' tuition here

Hence the Russians used to be able to tell if a player was any good or not even from the very first note.