Labour-run governments have "been a disaster" for Wales but not devolution itself, the Tories' Senedd leader says.
Paul Davies's comments follow reports PM Boris Johnson told Tory MPs that devolution was ex-Labour prime minister Tony Blair's "biggest mistake".
Mr Davies said Welsh ministers have "been obsessed with arguing about more powers" rather than public services.
First Minister Mark Drakeford said devolution "thrives" under UK Labour governments.
The prime minister was in a Zoom meeting on Monday night with Conservative MPs representing dozens of seats in northern England when he is said to have made the remarks.
The Sun website reported Mr Johnson had told the MPs "devolution has been a disaster" in Scotland.
In response, a Downing Street source said: "The PM has always supported devolution, but Tony Blair failed to foresee the rise of separatists in Scotland.
"Devolution is great - but not when it's used by separatists and nationalists to break up the UK."
Following a narrow victory in a referendum in 1997, the then prime minister Tony Blair's Labour government introduced devolution for Wales in 1999.
The assembly increased its powers considerably over the years and is now known as Senedd Cymru or Welsh Parliament.
Mr Davies, leader of the Conservatives in Cardiff Bay, said: "Devolution hasn't been a disaster.
"Twenty-plus years of Welsh Labour-led Governments have been a disaster for devolution in Wales. The people of Wales deserve better.
"Instead of doing their job in ensuring our economy and health and education services are the best they can be, the Welsh Government has been obsessed with arguing about more powers," he added.
Answering First Minister's Questions on Tuesday, Mr Drakeford said "devolution thrives when there is a Labour [UK] government to support it".
"You scratch the surface of the Conservative Party and all its old hostility to devolution rises back to the surface," the Welsh Labour leader told the Senedd.
"That's what happened yesterday, when the prime minister thought he could show off in front of a few Conservative MPs from the north of England."
Mr Drakeford was responding to a question from Plaid Cymru leader Adam Price.
Earlier, Mr Price said the prime minister calling the devolved governments "a disaster in the middle of this pandemic is a bit like Donald Trump accusing Joe Biden of being a danger to democracy."
He added: "Our "biggest mistake" is not leaving the Union sooner so we're saddled with you as PM - for now, but not for long."
Leader of the Abolish the Assembly Party, Richard Suchorzewski, said the prime minister "has now truly revealed what he believes about devolution".
"What a shame [Welsh Conservative] AMs/MSs have gone native," he tweeted.