I think a lot of this walk in/ambulance would have to do with the hospital you're at.
Do people in an ambulance still get triaged? Or do they just use info the ambo's have passed on? Maybe they do get triaged faster? I have no idea.
I've never been in a big city hospital ED.

I've walked in/driven myself more times than I can count, for dislocations, asthma attacks (I didn't know it was happening. Dd1's one & only & not severe), suspected sprains etc.
The only time I wasn't happy was when DD2 was severely dehydrated, at 4, with tonsillitis & glandular fever, with a temp that wouldn't come down under 39, when I could get dd to swallow panadol & we sat for 4 hours before she was even triaged. It was when I told them I'd have to take her home they finally got her through.
Her dehydration was at the point where they could not, & did not get a vein. But she went through hell with them trying :/

They probably had a lot going on that night, I don't know. Or we were forgotten about? But I don't think I've ever been quite that worried about one of my kids.

I do believe they do their best though. I also know there are people who go in for a bed for the night, or attention. That really doesn't help the system any.