This is actually what America would look like without gerrymandering

- Success (i.e. being voted in) is considerably easier when you depend on a proportion of the population than a majority, and this diminishes the power of party political vehicles.

- PR therefore encourages (or rather, discourages less) the formation of splinter groups, "forked" parties, and independent candidates

- It results in legislative bodies with no clear majority, which in turn leads to coalitions of convenience (great for mapping to population majority on single issues) but tends to destabilize governments that do not dance the dance of diplomacy very well (because tyrannical "we have a clear mandate" decisions don't work without a clear majority).

These are not necessarily bad features, because cooperation becomes regularly necessary rather than an occasionally inconvenient task. It does mean, however, that politicians have to be good at politicking to ensure they continue to be important in a world where loyalty to the party is only a piece of the whole pie.

If you add in STV (https://en.wikipedia.org/wiki/Single_transferable_vote) it gets even more interesting, because the transferable vote means each winner has to have the approval of a majority of the electorate. This means that, while in FPTP or simple PR, someone might get elected with (e.g. from parent comment) 17% of the vote (meaning that up to 83% of the population voted against them), in PR with STV, at least 50% + 1 has to approve of the candidate, to some extent.

Neither system removes the problem of gerrymandering however, because it's still possible to draw a constituency that is statistically going to maximize e.g. working class candidates, thereby reducing the impact of that electorate on neighbouring middle-class constituencies.