A “proportional vote” system relies on a complex mathematical formula to determine who is elected. The difficulty with this system is the ability to have a clear majority winner.
Without a majority, governments are forced into forming unstable, short lived coalitions which lead to constant elections.
It would be impossible to change back to “first past the post” if the proportional system was implemented and found to be worse. Italy has a history of this with elections nearly every year since the Second World War.
The proportional system is set up to get individuals elected and has nothing to do with an efficient functioning government system. Keep what we’ve got, it’s easy to understand and works better than anything else they have to offer.