Are you thinking of the same A1? I drive it regularly from the end of the A1(M) near Peterborough up to Doncaster. Lots of stretches with no hard shoulder. In fact, I'm struggling to think any bits with a hard shoulder but I'm sure there are some. Most slip roads are waaay shorter than motorway slip roads and there are loads of them, often with tight bends that unsight and slow down the joining traffic. It's incredibly un-motorway like. And to be fair, it doesn't spring to mind as a place where I see a lot of lunatic driving.
Not a place I'd go near on a bike. But also nothing like a motorway.
In fact I think I'd prefer to ride (illegaly) on hard shoulder of the A1(M) like the person in the OP than on the bits of A1 that I'm familar with. I imagine that would be a pretty safe place to be actually, if not exactly pleasant.
Back in January, doing a 3am loop, I was looking to turn onto the A40. Instead, I turned 150m too early, which would normally have been fine, because there's a gate across the road I turned into. Except it had been left open, and, therefore, the "Authorized Vehicles Only" sign on the back was impossible to see. So I'm tootling down this road, thinking it's a bit odd, I don't remember there being a bike lane? Wow, this is really wide, lovely!
Oh.
I'd unwittingly turned onto the M40.
Frankly, apart from the adrenaline and worrying that I was about to be pulled by an unmarked copper? Well, I can't say the mainline was fabulous, because even at that time there was a steady stream of occasional vehicles. But once off at the next exit, on a motorway spur? It was preferable to the dual carriageway A40 that it became, because there was a nice wide hard shoulder.
The A40 wasn't bad, don't get me wrong. Very few cars, I could take the left lane and they'd go past with no problems. But I was sure paranoid about making sure that my rear light was still working, whereas not being seen on the motorway might have been an advantage!
Point being, that, for the same road, I'd prefer the hard shouldered motorway version over the non-motorway version, from a safety standpoint. I can't make any direct comparisons with the main M40, but I didn't feel concerned about being hit from behind, where I would have done on a dual carriageway that busy.