Dense crumb problems when making sourdough baguette from natural yeast starter
I've been baking using a natural sounrdough starter I made from wild yeasts based on the Joy of Cooking recipe where you add 1/2 cup flour and 1/4 cup water every twelve hours over the course of a few days until it's bubbly and active from wild yeasts. I've tried a few different types of breads, but I'm mostly trying to make a white baguette with the sourdough starter as the only yeast.
With every loaf I have the same problem: the crumb is moist, chewy, and dense. The crust is amazing, the flavor is great, but always the crumb is very dense, even if it shows good fermentation and has some air holes inside, it always has a density that is unappealing. I am using only Heartland Mills  organic unbleached unenriched white flour, water, natural sourdough starter, and Real Salt brand salt. I have experimented with room temp and refrigerated rises, higher and lower dough hydration, more kneading and less kneading, the last time I used the dough hook only to combine the flour and water for the autolyse and then used the fold and stretch method to activate the gluten (three times at 20 minute intervals), &c.
The question I have is: does using an unenriched white flour rather than an all purpose flour limit the yeast's ability to work or is there something else going on?
The recipe I used last is below, I don't own a scale, so everything is in cups rather than by weight:
2 1/4 cups flour
1 cup filtered water (@tap temperature, about 68F)
1/2 cup natural sourdough starter
1/2 tbsp salt
Combine flour and water, autolyse for 20 min after combining in bowl using dough hook just long enough (approx 2 min) to combine ingredients. Add sourdough starter and salt, mix until combined (approx 2 min) then clean bowl using dough scraper and rest for 20 min. Fold dough in bowl using this method , rest 20 min, repeat this for a total of 3 folds resting 20 minutes between each fold. Move dough to oiled bowl for 4 hours at room temp (70F). Fold and stretch the dough in the bowl, and put in fridge for 14 hrs to rise. Remove from fridge, fold and stretch dough and let rest at 70F for 3 hrs. Cut and divide dough, shape and let rest for 20 min covered with plastic. Shape into baguettes and place in couche to rise. Rise for 3 hours at 70F. Move from couche to baking sheet covered in parchment paper. I have a hard time moving the dough from the couche as I have no peel to move them, but they still get a nice risen shape when baking.
Baking: 450 F for 30ish minutes, with two pans of water in the bottom of the oven for steam.
Anyone have any ideas why the crumb is so moist? I fear that I am not letting the dough rise enough in the couche, it seems to double in volume and when I press on the dough it makes a dent that stays, but still the lack of more spacious crumb has me wondering about this.
Unfortunately I don't have a photo of the crumb, but here's a photo of a loaf: