Chasing a revised 327 from 47 overs in the one-day game, the Red Rose lost their last nine wickets for 31 runs on their way to a 242-run thrashing.
It was Lancashire's heaviest defeat in List A cricket.
"I'm not going to be rip anyone in particular apart as it is a team effort, and it's not good enough," Giles told BBC Radio Lancashire.
"I do think there is a danger of thinking we're a better side that we are in one-day cricket, and we're not.
"We got away with it a little bit last year in T20 and in the end in 50 overs we almost qualified at the last minute, and we're doing the same thing again and we're not that good.
"Every time you go to play and wear that Lancashire shirt we've got to play better than that."
With Neil Wagner being called up by New Zealand for their Test series against Zimbabwe and South Africa, Giles has also spoken about the possibility of a replacement.
The Kiwi has taken 28 wickets so far this season after joining at the start of the campaign.
"We'll look at all the options but there needs to be the availability of the right person," Giles added.
"If there is then we'll certainly be interested. He'll be available for the next three Championship games and then missing until September."

David Cameron has refused to take part in the debates unless the Green Party is included.
Mr Clegg told the BBC he thought the debates would go ahead, but suggested the proposed format needed to change.
Earlier this week Mr Clegg, the deputy prime minister, said the broadcasters should grow a "backbone" and push ahead without Mr Cameron if necessary.
The plans put forward by the BBC, Sky News, ITV and Channel 4 in October would include the Conservatives, Labour, Liberal Democrats and UKIP.
One would feature a head-to-head between Mr Cameron and Labour leader Ed Miliband, another would also include Mr Clegg, and the third would feature the leaders of the Tories, Labour, Lib Dems and UKIP.
The suggested schedule is for debates on 2 April, 16 April and 30 April, ahead of the UK-wide poll on 7 May.
Mr Cameron has said all "national parties" must be represented at the live televised pre-election debates - which were first introduced for the 2010 general election.
Labour leader Ed Miliband has said it was a "pathetic excuse" to avoid the debates, but Mr Cameron said Mr Miliband was "chickening" out of debating the Greens.
On the BBC's Andrew Marr show on Sunday, Mr Clegg said Labour and the Conservatives were using the Greens as an "alibi" to block the debates.
"They want to put the genie back in the bottle. They want to run things as they've done before. I think it's too late," he said.
Mr Clegg, Mr Miliband and UKIP leader Nigel Farage have written to the prime minister saying it would be "unacceptable" for him not to appear.
In separate but identical letters sent earlier this week they urged the broadcasters to press ahead with the debate before the general election.
Mr Clegg said: "The broadcasters need to come forward with other proposals because clearly the current one - which I'm not wildly happy about because it excludes me as a leader of a governing party - so they need to come forward with a proposal.
"I'll get my soapbox out any day of the week."
Asked by Green Party in England and Wales leader Natalie Bennett - who was also on the programme - whether he would lobby for her party to be included, Mr Clegg said it was not for politicians to tell the broadcasters what to do.
Ms Bennett says the polls and public opinion support the argument for the Greens to be included.
Lancashire head coach Ashley Giles has questioned the attitude of his team after their record loss to Yorkshire.
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Lib Dem leader Nick Clegg has said the broadcasters should come up with "other proposals" for the TV election debates.