Overall, if done correctly there should be no issue with expressing the parties' intentions in plain English rather than using dense legalese. It's something I strive to do every day in my job for sure.
Of course I agree with your general point about laws being drafted to be precise and narrow, it's just that using legalese doesn't always secure this objective. Sometimes it's just clear that the draftsperson was having a bad day.
But they aren't that either.
There will always be more diversity in real life than on paper. You can't predict everything that will ever happen.
The real problem is structural.
We have a set of laws and if they're overly broad and prohibit lots of things they shouldn't, nobody really notices because prosecutorial discretion is a thing. As long as prosecutors mostly don't charge honest people with the overly broad laws, nobody gets up in arms to fix them even though everyone is in violation.
On the other hand, if someone does something unpopular and there is no law against it -- or there is a law against it but there isn't a law specifically against it and Something Must Be Done -- then we get a new overly broad law.
Laws get added but never removed, and each one prohibits more than it should. Over a hundred years of this and you get Three Felonies A Day, the only reason everyone isn't in prison is prosecutorial discretion, and lawyering is an exercise in figuring out which parts of which laws you actually have to follow to avoid being prosecuted without ever admitting that that's what's happening.
I don’t think that means they should be more narrowly defined than they are now. That would mean a permanent weapons race between those finding and exploiting loopholes and the government, with those having access to the smartest lawyers (= the richest) staying ahead of the law.
For example, if “income” would be restricted to money received in exchange for services, companies would start paying in goods, for example by providing “free” housing, cars, etc. if the government includes such things in the law, companies could start paying out in gold, rather than money. When that gets included, companies could sell special (extremely cheap, no voting rights, must sell when leaving the company) shares to personnel, and pay most of the salary in dividends. That list is endless. Companies could start operating under the flag of Liberia, claim that they don’t pay you for work done, but that they charge you for the use of their machines, and that you sell them the stuff you made with them, etc.
But in practice, it's the opposite. Law is full of ambiguities and loopholes. That's why we hire lawyers-- to find ones that work in our favor.
While laws being written in common language sounds like a good idea, common language is open to lots of ambiguity and loopholes. Shouldn't our laws, in general, be written to be as precise and narrowly defined as possible?