Newbie here... Overproofed? Help!

Hi All, my name is Lorena, I'm from Chile, and I'm a newbie in this tricky journey of sourdough. I made my starter around 1 and a half month ago.

My first loaf was pretty decent but oven spring didn't let me satisfied. It was baked in a dutch oven, straight from the fridge to the oven. At 250º C, 20 min and 220ºC, 20 min. This was the procedure:

Autolyse, rest 30 min, Levain, rest 30 min, Salt, rest 30 min. Bulk fermentation for 4 hours at 25ºC. During this time i performed 3 sets of stretch and fold every 15 min, and 3 every 30 min. Preshape, rest 30 min uncovered. Shape and chill for 19 hours. 

I used this %s

374 gr strong flour (11% protein with added gluten up to 13,8%), 55 gr whole wheat flour, 25 gr rye flour , 345 gr water, 9 gr salt, 92 gr levain.

For the second one, i tried a different method, following Full Proof Baking videos (kind of), using the same recipe. All the procedure was done in room temp (20ºC)

Autolyse, rest 4 hours. Levain, mix 3 min and rest 30 min. Salt, mix 3 min and rest 30 min. Strong fold, rest 30 min. Strong fold, rest 30 min. Lamination, rest 45 min. Coil fold 1, rest 45 min. Coil fold 2, rest 45 min.  Coil fold 2, rest the remaining of the bulk. Preshape, rest 20 min. Shape, rest 20 min. Chilled for 9 hours in the fridge. Baked in a homemade pizza stone with steam (lava rocks)

Although the first loaf had a nice crumb, the exterior is pretty much the same as the second one. And that's my main concern. Could it be the heat, or lack of? Both had different bulk fermentation times, at different temperatures. Maybe in both cases i over fermented? 

I've been looking for the causes of this over and over again, and apparently could be million reason! The starter, the temperature, the timings... I'm at lost here. 

I would really appreciate if you can point me in the right direction. Any insight guys?