That was an interesting experiment
For your information, when you added the 43 grams of extra flour, the dough formulation you used changed as follows:
|Occident Flour (100%):|
|338.82 g | 11.95 oz | 0.75 lbs|
251.45 g | 8.87 oz | 0.55 lbs
2.37 g | 0.08 oz | 0.01 lbs | 0.79 tsp | 0.26 tbsp
5.18 g | 0.18 oz | 0.01 lbs | 0.93 tsp | 0.31 tbsp
597.82 g | 21.09 oz | 1.32 lbs | TF = N/A
As you can see, you ended up with a hydration of about 74.2%, which is about what you have been using recently. That might help explain why the crumb looked similar, at least to me, to the crumb structure of your most recent efforts using 75% hydration. You will also note that the baker's percents for the salt and IDY also changed (decreased) because the total flour weight went up when you added the 43 grams of flour to the original amount. The dough balls you ended up with had the set of baker's percents noted above.
I hadn't thought much how you would actually knead the dough. I assumed that you might use the mixing/kneading regimen that was described in the article at https://sites.google.com/site/hollosyt/quickrusticciabattapizza
but with a rest period inserted in the middle of the knead and maybe a bit longer total knead time to account for the fact that your dough ball weight (about 555 grams initially) was more than the weight of the dough (about 490 grams) described in the article. I am also not sure about using cold water. In my experience, using cold water does make it difficult to form the dough. This is something that I learned when I tried to make dough that was to be frozen as soon as it was done mixing. Everything that I had read about how frozen dough balls are made commercially said to keep the dough as cold as possible at every stage.
With respect to your question about whether it is possible to knead the dough too much, maybe even to the point of rendering the dough unusable, the answer is yes. Some time ago I ran a test in which I intentionally tried to destroy a dough by overkneading. In my case, I used my food processor because of its high operating speed. You can read about that experiment at Reply 14 at http://www.pizzamaking.com/forum/index.php/topic,1187.msg10649/topicseen.html#msg10649
and at Reply 4 at http://www.pizzamaking.com/forum/index.php/topic,2964.msg25401/topicseen.html#msg25401