Italy certainly did [1]. In fact Italian politics became much worse since the proportional system was weakened.

[1] yes governments were weak and were replaced often, but that's a feature, not a problem.

What makes you believe that is desirable?

the belief that wider representation in the government, less polarization, a strong parliament and a weak executive is more desirable.

A weak executive would seem to reduce representation in government though?

As each member of parliament must necessarily represent the biggest groups in their constituencies.

So a decent size group scattered across many dozens of constituencies into relatively tiny groups would simply never get taken seriously without a strong executive.

No, you've got that exactly backwards. Parliament is the representation. Because of proportional representation, parliament represents all groups in the country, and not merely the majorities in each district.

What? Parliaments obviously cannot represent every group within any given country.

For example, non-residents, tourists, diplomats, etc..

You're right. Parliament represents only the entire electorate. And only really those opinions that are shared by enough people to be worth an entire seat. Still, it's far better representation than you get in a district system, where only local majorities of the electorate in each district are represented.

Exactly.

It's obviously not a silver bullet that will magically fix everything, but a lot of countries are doing very well with proportional representation.

Also, I think Italy actually has a hybrid system.

Positing moving from one extreme to another doesn’t avoid the fact that there’s plenty of middle ground.