Labour are not centrists, they are left wing, admittedly not radical left wing like they were under Corbyn, but definitely on the left. The Tories have gone off to the far right to cosy up to Reform and the traditional centrist party, the LibDems seems to have just gone slightly bonkers.
The LibDems maneuvred to pick up Tory seats (who had 'stolen' them from the LibDems in 2015). This is another stupidity of FPTP. Parties have to adapt to fit the dumbness of the voting system rather than standing for what they actually believe.
They are undoubtedly centrist, whether talking about cleaning up rivers, funding public services and reversing Brexit.
I'd agree Labour aren't far off, though sticking to Brexit for some dumb reason. It and Liz Truss have made it fairly impossible to fund public services.
This is not something that proportional representation will fix. Indeed, had it been in place at the last election, the radical far right reform party that got 14% of the vote but only 0.8% of the seats would have benefitted enormously.
There's a question whether far right parties deserve the representation that voters ask for. What I would say is if you deny it them, you're denying yourself democracy. Democracy just doesn't really exist when you have fewer than 5 parties that can win.
STV would deny Reform a few seats that MMP would give them though I suspect a better form of PR that properly caters for voting against the far right could be invented.