This is a crazy way of designing an assessment, mixing up being 'hard' with being 'rigorous' and using pass marks and grade attainment crassly.
All kinds of things can make a test harder and produce fewer high marks. We could wander round exam rooms sticking pins in pupils. This would make exams harder, but it wouldn't make them very rigorous, because the difficulties aren't coming from what is being assessed. The test has to be not whether it is hard, but whether it measures what is being assessed. An improved pass rate says ziltch about whether a test had become less rigorous-whether it accurately assesses what is being assessed. We don't argue driving tests should be made harder because most people eventually pass, we just want them to rigorously assess ability to drive.
Most people want exams that measure how quickly and effectively people can take in knowledge, and how skilled they are at applying it, because most people use their exam results not to follow up on the subject but as a general sign of aptitude in areas in which they get further training.
O-levels simply weren't that. They didn't reward bright pupils who were quick on the uptake because they tested at the end of a whole period of teaching when the slower kids who were bright-ish had caught up. They didn't reward application of knowledge because high marks could be obtained by regurgitating identikit answers. They didn't mirror how bright people work because nobody at the top of any profession is assessed on two-years work in two weeks. They were totally unfit for purpose as a sign of anything other than an ability to be schooled.
You can argue GCSEs need reform, but you have to do so in terms of what it is they are supposedly failing to test for, not simply 'to get fewer people to do well'. A return to O-levels is not that reform.