IMHO there are (broadly speaking) two types of MP's.
You have your typical party loyal "career" MP and then you have your "activists".
Much like Corbyn, Raynor is the latter.
They can be very useful within a party in terms of holding a mirror to itself, forcing uncomfortable debate and being somewhat fearless (or reckless depending on your view) with their own public image because fundamentally they are fuelled by a sense of righteousness re: their cause(s).
Yes, they may well garner some loyal supporters with whom they really resonate but they repel in equal (if not more) measure.
The issues arise when these MP's are elevated above the back benches.
They forget they are no longer just representing themselves, their constituents, their causes, but the party as a whole and now they have the platform where ALL the electorate is listening (not just the niche fringe groups).
If Labour were to win the next GE you would expect that AR as deputy would get a significant role in govt.
Whether you agree with what she said or not, most voters will not want the potential next Foreign Secretary (for example) to think it's ok to call the French (or any other) President scum, regardless of if it's true or not, because that's not appropriate statecraft.
As a member of the Shadow Cabinet you have to think of it as a bloody long job interview.
In other words you have to behave in a way that's appropriate to the position of power you aspire to hold.
AR does not do this. It's nothing to do with her accent, background or sex. Corbyn did not do this either and Starmer isn't doing a great job let's face it.
Having policies and fronting your party with people that are decidedly "marmite" doesn't get you elected, especially when the rhetoric is one of moral superiority whilst using aggressive language and in some cases trying to suppress reasonable debate.
Labour lost so many voters in the last election and I cannot see how anything they are doing right is is going to win them back.
Rather they are just making many "deserters" like myself feel more comfortable about not voting for them again.