Well, no… Anarchism can be achieved via parallel construction, provided that the existing society doesn't fight back. For example, mutual aid networks (as described by Peter Kropotkin). And an anarchist society could transition to a communist society (or pretty much any other society) – but even Friedrich Engels' "withering away of the state" route to communism (attributed to Karl Marx, but Wikipedia disputes that it was actually his idea) does not require the destruction of the existing society to precede communism.

I only have a superficial understanding of these ideas; but it seems to me that a good idea, whatever the ideology behind it, is worth implementing. And "we should make sure everyone gets fed by looking after each other" is a pretty good idea, so it shouldn't matter that it's technically "anarchy".

There are historical as well as contemporary examples of societies built on anarchist principles. They are few and fairly marginal, mostly because they tend to be crushed by the surrounding (centralized) cultures, but even so it's not all just hypothetical.

The most prominent contemporary example is the Zapatista territories. To a lesser extent, arguably also Rojava, although "libertarian market socialism" would probably be a more accurate label for that.

> Anarchist and Communists very much wanted a fundamentally different society,

They still want it.

> one so different that its essentially impossible to get there without destroying the existing one first.

Everything else they say is demagogy, in the end, all they are good for is fomenting strife and wars. After the bloodshed, these fools and their fantasies are quickly disposed of, the little tools they are.

Yes, you could have a corporation that does not have an internal hierarchy. But (in a left anarchist view) you cant have a corporation without private property and corporate limitation of liability. Both of those are (in their view) hierarchical.

The problem from a left anarchist standpoint isn't (just) "CEO is boss, having boss bad" its that there's a group of people with special treatment everyone else is not subject to.

You might disagree with that view, and probably do. I am just familiar enough with their ideas to relay and explain them.