'Serious parties have to be pragmatic and compromise in the centre-ish'
No, the centre has collapsed all over the world. Brexit, Trump, Farage, Corbyn are all indications that the centre has collapsed.
The centre is the Establishment - Ed Miliband, Blair and Cameron - and it has collapsed. The centre is the Establishment status quo where the Establishment wins and the people lose, where Panama Papers carry on and the people bail out the bankers who lobby the Establishment politicians. All of that has come to an end because people want change, an end to the status quo which is why all of the Establishment's helpers - Ed Miliband, the charidee brigade, Lord Pinnock, Blair, Cameron and all the rest of the 172 etc - can't prevent the tidal wave of Corbynism and "Momentum kids". it is over for the corrupt status quo and its servants, people want radical change of the system.
Corbyn offers radical change and that is why they are desperate to stop him.
Brexit is radical change and they wanted to stop that and they failed. Now they have failed to stop Corbyn and they won't stop "Momentum Kids" either.