I like the King Arthur too. Supposedly bread flour doesn't need extra gluten but it doesn't hurt to add some anyway IMO.
As Denny pointed out "crumb" is texture. I shoot for lots of big holes and firm cohesive texture. All purpose flour will result in a fragile crumb unless you really work it or add gluten. If you want more of a "wonder bread" type of crumb then don't let it proof for as long and don't make a poolish. You want a quick rise and a drier dough.
Oven spring... I want as much as I can get LOL. Gluten helps keep in the co2 which will expand in the oven blowing up the dough even more before it sets. This is where it can get tricky. Proof too long and it'll collapse in the oven or when you handle it. If you don't slash your dough deep enough it'll retard the spring and maybe rip your loaf open since the outside cooks before the inside creating a type of shell that compresses the expanding dough inside.
Baguettes work well because they can expand more fully before the exterior crust becomes rigid. Conversely, a big loaf has a lot of mass so in cross section you'll see fine bubbles in the center and outwardly they'll get bigger. The loaf won't spring effectively and maybe even rip.
I shoot for a dough that is very elastic and fairly sticky. If it can be handled easily without extra flour then it's probably too dry and will result in a denser loaf.
It's like brewing. One's technique matters and I only covered part of it.