This means employees get let go with legal bare minimum compensation and have little (if any) legal position to fight back.
Immoral but not illegal.
I don't know what country you're posting this from, but in the US none of this matters, and it does not apply. When someone is let go there is no "legal bare minimum compensation." There are some notice requirements (e.g. the WARN act), and many companies will pay out compensation in lieu of notice if the WARN act applies, but an acquisition makes no difference to these notice requirements.
The US culture of "at will employment" (i.e fire you on the spot for little reason) gives me anxiety and I don't even live there!
Note that I said lay off not fire above. There is an important legal difference.
My former job laidoff few people because of high paying salary. They got high salary because positions required a specialized and niche knowledge for their jobs. They are good at what they do which earned their justification for high paying. It took the company a year to hire a barely qualified person because they don't want to increase the pay after declined job offers from multiple potential candidates.
so what is the difference?
a layoff is due to business "loss" or changes? How is that really any different to a firing?
Laid off just means they don't need the job done anymore, and has nothing to do with how good or bad you are.
Eh, in theory maybe. Not really in practice. When layoffs happen, companies often prioritize laying off lower performers. And they often still need the jobs done, just fewer people.
Of course none of these are legal differences. The legal difference I know of is that being fired for cause affects whether you are eligible for unemployment insurance benefits.
"to let go" means redundancy.
It appears some countries see little difference between the two and others have a clear distinction and legal process.
Because it turns out that is what employers do. That's why most countries have have laws preventing employers from arbitrarily dismissing employees unless you have an actual reason.
If you have a bad employee, you can fire them. You don't need at will employment for that. Unless you mean "I don't like this employee, who is doing their job properly" in which case you don't have a bad employee, you're an asshole.
[1] If you're ever fired and your employer claims they're allowed to do so because "at will" employer, note that "at will" only covers "legal" reasons. Retaliation, bias, anti-pregnancy, anti-child, anti-religion, etc are all illegal reasons. Always ensure that everything you communicate with your employer is in writing. As @nxm is demonstrating your only safe option is to assume that your employer is your enemy.