Dropping your weapon is not defined anywhere in the PHB. Like many things outside of the defined rules, it's up to the DM to make a ruling on how to handle it. You could rule that every time you drop your weapon you have a chance to damage or even break it. The PC's opponents could ready an action to pick up or smash the weapon after the first time the caster does it. As a DM you are within your rights to simply say "No, that's dumb I don't allow it".
First off, the "you can always say no, so the rules don't need to be changed like ever" is a dumb excuse. Yes, I can always make on-the-cuff rulings, but that completely misses the point:
that I should not have to.
5th edition doesn't deserve labyrintine rules like these. And this thread is expressly about imagining the game without them.
That said, you're wrong: take disarming for instance. The PHB defines disarming a target as forcing it to drop one item of your choosing. The object lands at the creature's feet. No mention of anything breaking or getting damaged. (Which makes sense assuming we're talking about weapons of war, not porcelain vases) So no, the DM doesn't have to make a ruling, she can just use common sense to read the PHB and assume the RAI is "the object is now at your feet, ready to be picked up again"
But if you want to fix it, you need a goal. All the word-smithing in the world isn't going to change anything if you don't know what your target is.
Which is why I say you can either follow the rules as written, change how you interact with objects or change the way somatic materials work. But you have to decide on the goal first.
Why do you keep saying this despite me being excessively clear about my goals?
Everybody else in the thread understands. What is it about the current rules that you can't let go of? Why do you refuse to acknowledge my goals - they're really really simple.
Imagine the PHB is blank on the subjects of hand use, object interaction and spell components.
Now it's
your task, Oofta, to write up a set of rules that result in characters doing much the same things the PHB allows them to, yet avoids loopholes such as the ones we have been talking about.
I should tell you, I simply won't believe it if you say you would end up with the same ruleset as today's - I absolutely believe you're much better than that. Remember, a clean slate. No copying existing chunks of text. Would you, as the new star 5e designer, really start writing fiddly rules (that you later spread out all over the book) about which hand goes where, and how some but not all focuses can do double duty when used in highly specific component combinations? I have faith in you.