FWIW I started out with open sights, as a lot of people did. I had been shooting for several years before I owned a scope, and even now, 40 years later, I have several rifles without scopes.

As I enter my 50s I have to say that open iron sights are getting harder to use, especially in lower light. As someone said above, a lot of factory opens are poorly designed too, which doesn't help, but a good wide square notch and a square post, the design I have on a couple of rifles, works reasonably well - good enough to plug a pig or deer at maybe 100 yards anyway.

Better still is an aperture sight, and I have several rifles with these. They work fine for the sort of distances I'd usually shoot game - far more often at under 200 yards than over 200. I've shot with aperture sights on the range out to 1000 yards, and IMHO as long as you can see a reasonably distinct aiming mark they give away little in accuracy to a hunting scope. By way of actual comparison on my .45/70 the groups with a scope on 5x were about 1 1/4" at 100 yards, and about 1 1/2" with a peep.

Undeniably the scope is better in very low light though. Better when the target is hard to make out too, whether because it is obscured by cover or the same colour as the background. I've found that a low magnification scope is also very fast to use - fast enough to shoot clay pigeons when mounted on my combination or drilling, and certainly fast enough to bowl over running game - I don't think that open sights have any advantage at all in this regard, at least for me.

The main area where, at least in my own experience, a scope falls down compared to aperture or even open sights is in rain. Rain on the lenses, or fogging on the exterior from my own breath in wet conditions, has cost me opportunities, though some of the newer coatings seem to be an improvement.

The scope also adds weight of course, but not much with the smaller scopes I prefer, and needs a bit more looking after than a solidly-made set of open or peep sights.

Possibly the best solution, and the one I have on several hunting firearms, is a scope which can be detached quickly by hand, and replaced without losing zero, backed up by a good aperture or open sight setup (which is also properly zeroed of course). That way if I have a bad spill, or it starts raining, I can take the scope off and keep hunting.